Anti-angiogenic polypeptides

ABSTRACT

Anti-angiogenic polypeptides A 61  or p22 are disclosed. Also disclosed are methods of making the polypeptides and methods of treating subjects having angiogenic diseases or conditions.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. application Ser. No. 60/253,725 filed Nov. 28, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to angeogenesis and, more particularly, to anti-angeogenic polypeptides which are related to plasminogen and to methods of making and using such polypeptides.

2. Description of the Related Art

Angiogenesis, i.e. the formation of new blood vessels, involves a complex coordination of endothelial cell proliferation, migration, basement membrane degradation and neovessel organization (Ji et al., FASEB J. 12:1731-1738, 1998). During normal processes such as organogenesis in the embryo and wound healing in the adult, angiogenesis provides the necessary vascular support for the newly developing tissue. In pathologic conditions, however, the growth of new blood vessels can lead to advancement of disease processes including the development and progression of cancerous tumors, diabetic retinopathy, tissue and organ malformation, and cardiovascular disorders (Folkman, Nat. Med. 1:27-31, 1995). With respect to cancerous tumor, increasing evidence suggests that tumor growth and lethality are dependent upon angiogenesis and that angiogenesis inhibition suppresses tumor development (Folkman, Forum (Genova) 9:59-62, 1999; Folkman, Adv. Cancer. Res. 43:175-203, 1985).

A number of angiogenesis inhibitors, i.e. anti-angiogenic substances have been identified including angiostatin, thrombospondin, and glioma-derived angiogenesis inhibitory factor (Folkman, 1995 supra). Of these, angiostatin, a 38 kDa fragment of plasminogen, has been shown to have potent anti-angiogenic activity which inhibits tumor growth (O'Reilly et al., Nat. Med. 2:689-692, 1996; O'Reilly et al., Cell 79:315-328, 1994). This is in contrast to the full length plasminogen which has no anti-angiogenic activity (Id.).

Angiostatin contains the first four of plasminogen's five triple disulfide-linked loops known as kringle regions. The four kringle regions of angiostatin and the fifth kringle region found in plasminogen, but not angiostatin, have been characterized as to anti-angiogenic activity by studying the activities of various fragments of plasminogen. Kringle 5 fragments of plasminiogen obtained by proteolyisis of plasminogen and by recombinant techniques have been reported to exhibit potent endothelial-cell anti-proliferative activity (Cao et al., J. Biol. Chem. 272:22924-22928, 1997). Similarly, a recombinant kringle 1 fragment and a recombinant kringle 3 fragment have been shown to have potent anti-proliferative activity whereas a kringle 2 fragment shows much less inhibitory activity and a kringle 4 fragment exhibits markedly low inhibitory activity (Cao et al., J. Biol Chem. 271:29461-29467, 1996; U.S. Pat. No. 6,024,688 to Folkman et al.). In contrast, a fragment containing kringles 2 and 3 showed only low activity, whereas a larger angiostatin fragment containing kringle regions 1-3 showed more potent anti-proliferative activity than angiostatin itself which contains kringle regions 1-5 (Id.).

Thus, it would appear that the anti-angiogenic activity of plasminogen fragments containing more than one kringle region cannot be accurately predicted based upon the activities of the individual kringle regions and, hence, the earlier studies provide no clear guidance as to whether additional fragments of plasminogen containing more than one kringle region will show anti-angiogenic activity. In addition, angiostatin itself was isolated under reducing conditions such that this substance is believe to a non-naturally occurring fragment as are the proteolytic and recombinant fragments reported in the earlier studies cited above. Such non-naturally occurring polypeptides could potentially elicit immunologic responses in a subject or other undesirable side effects which might be avoided with a naturally occurring fragment. Furthermore, the three dimensional structure of a naturally occurring fragment of plasminogen which functions as an endogenous angiogenic agent may not be accurately predicted from the three dimensional structure of the reported proteolytic or recombinant fragments in earlier reports. It would, thus, be desirable to identify and isolate new, naturally occurring polypeptide fragments of plasminogen which possess potent and efficacious anti-angiogenic activity and which have little or no potential for producing immunologic and other side effects.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the inventors herein have succeeded in discovering new, naturally occurring fragments of plasminogen. One such fragment, referenced herein as A₆₁, has a molecular weight of approximately 61 kDa as determined by SDS-polyacrylamide gel electrophoresis conducted under reducing conditions (Kassam, G. et al., (2001) Journal of Biological Chemistry 276: 8924-8933). Human A₆₁ has 391 amino acids the sequence of which is set forth in SEQ ID NO:1. A second naturally occurring fragment which is a minor variant isoform of A₆₁ is formed by cells from plasminogen in small amounts with A₆₁. This isoform contains 394 amino acids and has the sequence as set forth in SEQ ID NO:2. This variant isoform is included within the term A₆₁ as used herein. A third naturally occurring fragment, referenced herein as p22, has also been identified (Kwon, M. et al., (2001) Biochemistry 40: 13246-13253). P22 has a molecular weight of approximately 22 kDa. Human p22 has 103 amino acids and its sequence is as set forth in SEQ ID NO:3. The full length plasminogen human sequence from which the fragments are derived is shown in FIG. 1 and in SEQ ID NO:4. A₆₁, its minor variant and p22 all exhibit anti-angiogenic activity inhibiting endothelial cell proliferation in vitro and in vivo, and show anti-cancer activity in vivo.

The present invention is intended to include all A₆₁ and p22 molecules from a variety of vertebrate species, more preferably from mammalian species and most preferably from humans. Sequences from non-human species can be readily identified from the known plasmin and plasminogen sequences of a wide variety of species. Allelic variants of A₆₁, and p22 are also included within the present invention.

A₆₁ and p22 differ from angiostatins in several respects. First, both A₆₁ and p22 are naturally occurring molecules found in the blood plasma of both healthy individuals and in cancer patients. Second, they are both cleavage products of plasmin autodigestion, and, therefore, amino terminals and carboxy terminals are determined by the presence of plasmin cleavage sites within the plasminogen molecule. Unlike angiostatins, human p22 extends from Lys-78 to Lys-180 of plasminogen, thereby comprising 103 contiguous amino acids of plasminogen, and human A₆₁ extends from Lys-78 to Lys-468, and also includes a minor species extending from Lys-78 to Arg471, thereby comprising 391 and 394 contiguous amino acids, respectively. Thus, p22 contains the kringle 1 region plus a portion of the kringle 2 sequence of plasminogen and A₆₁ contains kringle regions 1-4 and a portion of kringle 5 sequence of plasminogen.

Also unlike angiostatins, these fragments can be prepared from plasmin or plasminogen in vitro in the absence of a free sulfhydryl donor or a plasmin reductase. And because of the ready availability of human plasminogen and the autoproteolytic nature of plasmin conversion to p22 and A₆₁, the fragments are easily prepared in milligram quantities, either in a cell-free system or by contacting the plasminogen to cells. The p22 and A61 polypeptides are isolated from cells cultured in the presence of plasminogen using standard techniques well known in the art, such as affinity chromatography using immobilized lysine or a lysine analogue capable of binding plasmin, hydrophobic interaction chromatography, gel filtration chromatography, and ion-exchange chromatography. Affinity chromatography with other immobilized ligands, such as (but not limited to) antibodies to plasminogen kringle domains can also be used. P22 exhibiting anti-angiogenic activity is found in both flow-through and eluted fractions when immobilized lysine is used for the isolating, and is also found in flow-through fractions when hydrophobic interaction chromatography is used for the isolating, wherein octyl-Sepharose is used as the hydrophobic solid-phase matrix.

These fragments also differ by their spectral characteristics from angiostatins and other plasminogen fragments described as having anti-angiogenic activity. In particular, the differences in autofluorescence and circular dichroism spectra indicate that the kringle domain of p22 is conformationally distinct from that of recombinant kringle 1. The circular dichroism spectrum of p22 exhibits a positive band at 227.5 and a negative band at 202.7 compared to a positive band at 227.5 and a negative band at 197.4 for the kringle 1 fragment. This indicates that the three dimensional structure of p22 differs from that of the kringle 1 fragment of plasminogen.

These fragments also differ from angiostatins in terms of their biological activity. When inhibition of bovine capillary endothelial cell proliferation is used as an assay system, A₆₁ requires about 35 nM for 50% inhibition of cell proliferation, whereas p22 requires about 14 nM for 50% inhibition of cell proliferation. In addition, both p22 and A₆₁, inhibit metastatic tumor growth in vivo using a Lewis lung carcinoma cell assay in mice as a model system. In contrast to angiostatins, both p22 and A₆₁ are effective in inhibiting growth of lung metastatic loci at a dose of about 2.5 mg/kg/day. A₆₁ and p22 can, thus, be used in the treatment of cancerous tumors in humans and other mammals.

Thus, in one embodiment, the present invention is directed to isolated and purified fragments of plasminogen which are A₆, and p22 polypeptides. The fragments can be identified by virtue of their sequence alignment with human plasminogen as set forth in SEQ ID NO:4, wherein the amino terminal amino acid is Lys-78 and the carboxy terminal amino acid is Lys-180 (p22), Lys468 (A₆₁), or Arg-471 (A₆₁ minor variant) of human plasminogen. The fragments are naturally occurring and fragments from non-human species have at least 60%, preferably, at least 75%, more preferably, at least 80%, still more preferably at least 90% and most preferably at least 95% sequence identity with plasminogen as set forth in SEQ ID NO:4.

In another embodiment, isolated A₆₁ and p22 polypeptides are provided which consist of 102, 391 or 394 amino acids of the amino terminal of plasmin. The plasmin can be a vertebrate plasmin, more preferably, a mammalian plasmin and, most preferably, a human plasmin. A human plasminogen has a sequence as shown in FIG. 1 and in SEQ ID NO:4. The polypeptides of this embodiment have at least 60%, preferably, at least 75%, more preferably, at least 80%, still more preferably at least 90% and most preferably at least 95% sequence identity with plasminogen as set forth in SEQ ID NO:4.

In yet another embodiment, isolated A₆₁ and p22 polypeptides are provided having have sequences as set forth in SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3, or conservatively substituted variants thereof. By conservatively substituted variant it is meant that the polypeptide has one or more conservative amino acid substitutions compared to the sequences of SEQ ID NOS:1-3. Conservative amino acid substitutions refer to the interchangeability of amino acids having similar chemical properties as a result of having similar side chains.

The present invention provides, in another embodiment, isolated A₆1 and p22 polypeptides which have at least 60%, preferably, at least 75%, more preferably, at least 80%, still more preferably at least 90% and most preferably at least 95% sequence identity with A₆₁, or p22 sequences. The isolated polypeptides can consist of 391 contiguous amino acids having have at least 60%, preferably, at least 75%, more preferably, at least 80%, still more preferably at least 90% and most preferably at least 95% sequence identity with SEQ ID NO:1; or the isolated polypeptides can consist of 394 contiguous amino acids having at least 60%, preferably, at least 75%, more preferably, at least 80%, still more preferably at least 90% and most preferably at least 95% sequence identity with SEQ ED NO:2; or the isolated polypeptides can consist of 103 contiguous amino acids having at least 60%, preferably, at least 75%, more preferably, at least 80%, still more preferably at least 90% and most preferably at least 95% sequence identity with SEQ ID NO:3.

In another embodiment, the invention also provides conjugates of an A₆₁ or p22 polypeptide and a cytotoxic agent in which the A₆₁ or p22 polypeptide provides not only an antiangiogenic effect, but also serves to target a regions eliciting angiogenic growth such as a growing tumor. The conjugate can, in some instances, be a fusion proteins and nucleic acid molecules encoding such fusion proteins are also included as are vectors and cells transformed with such nucleic acid molecules.

In another embodiment, the invention provides an A₆₁ or p22 nucleic acid molecule comprising a polynucleotide sequence which encodes an isolated A₆₁ or p22 polypeptide. The sequence encodes an A₆₁ polypeptide consisting of 391 contiguous amino acids and the polynucleotide sequence contains a sequence of not more than 1173 consecutive nucleotides of a sequence encoding plasminogen. Alternatively, the sequence encodes an A₆, polypeptide consisting of 394 contiguous amino acids and the polynucleotide sequence contains a sequence of not more than 1182 consecutive nucleotides of a sequence encoding plasminogen. As still another alternative, the sequence encodes a p22 polypeptide consisting of 103 contiguous amino acids and the polynucleotide sequence contains a sequence of not more than 309 consecutive nucleotides of a sequence encoding plasminogen. The invention also provides vectors comprising the nucleic acid, and eukaryotic and prokaryotic cells comprising the vector. The cells can be mammalian cells. The mammalian cells can be, for example, human, murine, or bovine cells. The prokaryotic cells can be bacterial cells. The bacterial cells can be, for example E. coli cells. In addition, the vector can be, for example, a plasmid or a virus.

In another embodiment, the invention provides an A₆₁ or p22 nucleic acid or complement thereto consisting of 309, 1173, or 1182 nucleotides, wherein the nucleic acid has at least 90% identity with SEQ ID NO:5, SEQ ID NO:6, or SEQ ID NO:7, respectively. In an alternative embodiment, the nucleic acid of 309, 1173 or 1182 nucleotides hybridizes under high stringency conditions to SEQ ID NO:5, SEQ ID NO:6, or SEQ ID NO:7, respectively.

The invention also provides methods for preparing A₆, and/or p22 polypeptide fragments of plasminogen. A₆₁ and p22 can be produced by a cell-mediated method or in a cell-free method. The cell-mediated method comprises contacting a plasminogen with a vertebrate cell which upon incubation, produces the A₆, and/or p22 fragments of plasminogen by autoproteolysis. The A₆₁ or p22 fragments are then isolated from the mixture. Cells are preferably mammalian cells, preferably human cells such as HT1080 or HeLa cells. Another preferred cells for use in the method is a bovine capillary endothelial cell. The plasminogen can be a glu-plasminogen or a lys-plasminogen. The isolation can be by any suitable approach including affinity chromatography using immobilized lysine or an immobilized lysine analogue capable of binding plasmin to contact the plasminogen fragment. Further purification can be through other chromatography techniques, such as hydrophobic interaction chromatography and gel filtration chromatography.

In the cell-free method, first A₆₁ is produced by incubation of a mixture of plasminogen with plasminogen activator. A₆₁ is then isolated from the mixture. p22 is then produced from the A₆₁ upon incubation with plasmin and a reducing agent such as dithiothreitol. The p22 is isolated from the incubation mixture. Alternatively, p22 can be produced by incubating A₆₁ with annexin II subunit of annexin II tetramer.

The present invention also provides methods for anti-angiogenic treatment of a mammal in need thereof. The methods comprise administering an angiogenesis-inhibiting amount of a A₆₁ and/or p22 to the mammal. The method is applicable to any disease or condition involving unwanted angiogenesis, in particular the growth of tumors in cancer. The mammal is, preferably, a human and the A₆₁ and/or p22 are, preferably, human polypeptides. The A₆₁, and/or p22 can also be administered in combination with other agents to treat the particular disease such as, for example, other anti-cancer agents for treating cancer.

In yet another embodiment, the invention provides for a method of inhibiting the proliferation of vascular endothelial cells. The method comprises administering to the cells A₆₁ or p22 or a combination thereof in an amount suitable for inhibiting endothelial cell proliferation.

Among the several advantages achieved by the present invention, therefore, may be noted the provision of new anti-angiogenic agents which are useful in treating diseases involving neovascularization which is deleterious to the individual such as occurs with cancerous tumors; the provision of anti-angiogenic agents which are naturally occurring and as a result present less risk of immnunologic response to an individual receiving the agent; the provision of anti-angiogenic agents which are efficacious and which present less potential for undesirable side effects by virtue of their being substances which occur naturally in the individual receiving the agent; the provision of methods for preparing the new anti-angiogenic polypeptides which are simple to perform and which achieve a high yield of the polypeptides; and the provision of new and effective methods for treating diseases involving angiogenesis based upon administration of the new compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the amino acid sequence of human plasminogen precursor in which amino acids Met-1 to Gly-19 (M-1 to G-19) are the signal peptide; amino acids from Glu-20 through Asp-810 (E-20 to N-810) are glu-plasminogen; amino acids from Lys-97 through Asp-810 (K-97 to N-810) are lys-plasminogen; amino acids from Lys-97 through Lys-487 (K-97 to K487) and amino acids from Lys-97 through Arg-490 (K-97 to R-490) are the two isoforms of A₆₁; and amino acids from Lys-97 through Lys-199 (K-97 to K-199) are p22.

FIG. 2 illustrates the nucleic acid sequence of human plasminogen precursor in which nucleic acids 55-111 encode the signal peptide; nucleic acids 112-2484 encode the glu-plasminogen; nucleic acids 343-2484 encode the portion of glu-plasminogen forming lys-plasminogen; nucleic acids 343-1515 and nucleic acids 343-1524 encode the portion of glu-plasminogen or lys-plasminogen forming the two A₆₁ isoforms; and nucleic acids 343-651 encode the portion of glu-plasminogen or lys-plasminogen forming p22.

FIG. 3 illustrates the generation and isolation of A₆₁ produced in a cell-free system as analyzed in reduced SDS-PAGE with Coomassie Blue staining (A), in non-reduced SDS-PAGE with Coomassie Blue staining (B), and by Western blotting using a monoclonal antibody against human plasminogen kringles 1-3 as the primary antibody (C).

FIG. 4 illustrates the time course of plasminogen cleavage to form A₆₁, as analyzed in reduced SDS-PAGE with Coomassie Blue staining (A) and in non-reduced SDS-PAGE with Coomassie Blue staining (B).

FIG. 5 illustrates Western blots comparing A₆₁, and plasminogen fragments present in mouse sera using rabbit anti-mouse angiostatin antibody (A) or monoclonal anti-human plasminogen kringle 1-3 antibody (B).

FIG. 6 demonstrates that detectable levels of an A₆₁-like plasminogen fragment are present in serum from normal, tumor-bearing, and tumor-resected mice

FIG. 7 illustrates a comparison of A₆₁ with plasminogen fragments present in sera from normal volunteers (A) or cancer patients (B).

FIG. 8 illustrates the circular dichroism spectrum of A₆₁.

FIG. 9 illustrates the intrinsic fluorescence spectra of A₆₁ in the absence and presence of Trans-4-aminomethylcyclohexanecarboxylic acid (AMCHA).

FIG. 10 illustrates the inhibition of bovine capillary endothelial cell proliferation by A₆₁.

FIG. 11 illustrates the inhibition of metastatic tumor growth by A₆₁ in mice injected subcutaneously with Lewis lung carcinoma cells as measured by Lung weight over time.

FIG. 12 illustrates the generation of p22 in a cell-free system.

FIG. 13 illustrates the identification of a novel plasminogen fragment (p22) produced by HT-1080 cells.

FIG. 14 is a diagrammatic illustration of the structure of p22.

FIG. 15 illustrates the circular dichroism spectra of p22 and kringle 1 (K1).

FIG. 16 illustrates the intrinsic fluorescence spectra of p22 and recombinant K1.

FIG. 17 illustrates the inhibition of bovine capillary endothelial cell proliferation by p22 and recombinant kringle 1.

FIG. 18 illustrates the inhibition of neovascularization on the chick chorioallantoic membrane (CAM) by p22.

FIG. 19 illustrates the inhibition of metastatic tumor growth in mice lungs.

FIG. 20 illustrates the binding of A₆₁ to annexin II tetramer.

FIG. 21 illustrates the decrease in p22 and A₆₁ production in HeLa cells transfected with an expression vector containing antisense to p11 subunit of annexin II tetramer.

FIG. 22 demonstrates that the generation of p22 from A₆₁ requires plasmin and annexin II tetramer.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, new, naturally occurring fragments of plasminogen have been discovered. The new polypeptides are referenced herein as A₆₁ and p22. These polypeptides exhibit anti-angiogenic activity and as such they are useful in compositions for the treatment of diseases and conditions involving an unwanted and deleterious neovascularization.

Plasminogen is a single-chain glycoprotein present in plasma at a concentration of about 2 μM (Wohl et al., Thromb. Res. 27:523-535, 1982; Kang et al., Trends Cardiovasc. Med. 90:92-102, 1999). The human plasminogen polypeptide of which contains 791 amino acid (FIG. 1, amino acids 19-810). Native glu-plasminogen is readily converted to lys-plasminogen by plasmin hydrolysis of the Lys-77-Lys-78 bond (FIG. 1, amino acids 97-810). Plasminogen serves as a precursor to plasmin which is a protease formed by cleavage of plasminogen between Arg-561 and Val-562 by tissue plasminogen activator or urokinase-type plasminogen activator. Disulfide bridges form covalent bonds that link the two polypeptide chains of plasmin together. The larger polypeptide chain or plasmin A chain, which is also cleaved between Lys-77 and Lys-78 of plasminogen to form a chain of Lys-78 through Arg-561, contains five kringle domains while the smaller or B chain is formed from Val-562 through Asp-791 of plasminogen. Both plasminogen and plasmin bind to fibrin through amino-terminal kringle regions each of which is a triple loop region formed as a result of disulfide bonds. As used herein, the term “plasminogen” is intended to include human glu-plasminogen and lys-plasminogen as well as allelic variants of the human sequences. Also included are plasminogen orthologs from non-human mammalian species as well as from non-mammalian vertebrate species, a large number of which are known in the art.

The A₆₁ and p22 polypeptides and polynucleotides of the present invention correspond to portions of the polypeptide sequences and polynucleotide sequences, respectively, of plasminogen. The term “corresponds to” is used herein to mean that a that a polypeptide sequence is identical to a reference polypeptide sequence or a polynucleotide sequence is homologous (i.e., is identical, not strictly evolutionarily related) to all or a portion of a reference polynucleotide sequence. In contradistinction, the term “complementary to” is used herein to mean that the complementary sequence is not identical to the reference sequence, but comprised of a sequence of purine and pyrimidine bases precisely matched to the pyrimidine and purine bases, respectively of the reference sequence. For illustration, the nucleotide sequence “TATAC” corresponds to a reference sequence “TATAC” and is complementary to a reference sequence “GTATA”.

A₆₁ has a major and a minor polypeptide isoform, the major isoform having a sequence of 391 amino acids (SEQ ID NO:1) from Lys-78 to Lys-468 of plasminiogen and the minor isoform having a sequence of 394 amino acids (SEQ ID NO:2) from Lys-78 to Arg-471 of plasminogen. Although the human A₆₁, isoforms are identified as portions of human plasminogen, it is intended that the term A₆₁ include orthologous sequences from non-human mammalian species as well as from non-mammalian vertebrate species. The sequences of such orthologous A₆₁ molecules can be readily determined by alignment of orthologous plasminogen sequences with human plasminogen and then identifying the portion of the molecule that represents A₆₁, polypeptides. Alternatively, putative orthologous A₆₁, polypeptides can be aligned with human A₆₁. It is believed that non-human mammalian orthologous A₆₁ polypeptides will have at least 75% sequence identity, i.e. at least 75% identical amino acids, as compared to human A₆₁ and that non-mammalian vertebrate orthologous A₆₁ polypeptides will have at least 60% sequence identity as compared to human A₆₁, polypeptides.

The p22 polypeptide has a sequence of 103 amino acids (SEQ ID NO:3) from Lys-78 to Lys-180 of plasminogen. Although the human p22 is identified as a portion of human plasminogen, it is intended that the term p22 include orthologous sequences from non-human mammalian species as well as from non-mammalian vertebrate species. The sequences of such orthologous p22 molecules can be readily determined by alignment of orthologous plasminogen sequences with human plasminogen. Alternatively, putative orthologous p22 molecules can be aligned with human p22. It is believed that non-human mammalian orthologous p22 polypeptides will have at least 75% sequence identity, i.e. at least 75% identical amino acids, as compared to human p22 and that non-mammalian vertebrate orthologous p22 polypeptides will have at least 60% sequence identity as compared to human p22.

Methods of sequence alignment for identifying homologous sequences which can be either paralogs or orthologs are well known in the art. For example, two or more sequences can be aligned using the Clustal method (Higgins et al, Cabios 8:189-191, 1992) of multiple sequence alignment in the Lasergene biocomputing software (DNASTAR, INC, Madison, Wis.). In this method, multiple alignments are carried out in a progressive manner, in which larger and larger alignment groups are assembled using similarity scores calculated from a series of pairwise alignments. Optimal sequence alignments are obtained by finding the maximum alignment score, which is the average of all scores between the separate residues in the alignment, determined from a residue weight table representing the probability of a given amino acid change occurring in two related proteins over a given evolutionary interval. Penalties for opening and lengthening gaps in the alignment contribute to the score. The default parameters used with this program are as follows: gap penalty for multiple alignment=10; gap length penalty for multiple alignment=10; k-tuple value in pairwise alignment=1; gap penalty in pairwise alignment=3; window value in pairwise alignment=5; diagonals saved in pairwise alignment=5. The residue weight table used for the alignment program is PAM250 (Dayhoff et al., in Atlas of Protein Sequence and Structure, Dayhoff, Ed., NBRF, Washington, Vol. 5, suppl. 3, p. 345, 1978).

Human A₆₁, polypeptides are further characterized in that they have a molecular weight of approximately 61 kDa as determined by SDS-polyacrylamide gel electrophoresis conducted under reducing conditions. Circular dichroism, which examines the secondary structure of molecules revealed that A₆₁ polypeptides exhibited a strong negative band at 202 nm and a weak positive band at about 227 nm. Analysis of secondary structure content suggested the presence of kringle-containing structures and capable of binding to free or C-terminal lysine residues. A₆₁ polypeptides are biologically active in inhibiting endothelial cell proliferation showing a concentration required for 50% inhibition (IC₅₀) to be 35±10 nM in in vitro cultured bovine capillary endothelial cells. Moreover, A₆₁ polypeptides at a dose of 2.5 mg/kg, i.p. inhibited metastatic tumor growth in mice challenged with Lewis Lung carcinoma cells.

Human p22 is further characterized in that it has a molecular weight of approximately 22 kDa as determined by SDS-polyacrylamide gel electrophoresis conducted under reducing conditions. Circular dichroism revealed that p22 exhibited a strong negative band at 202.7 and a positive band at 227.5 nm. In contrast, a recombinant kringle polypeptide exhibited a strong negative band at 197.4 nm and positive band at 227.5 suggesting that p22 has a different secondary structure from that of the recombinant kringle 1 polypeptide. Evaluation of the biological activity of p22 revealed that it inhibits endothelial cell proliferation in cultured bovine capillary endothelial cells at an IC₅₀ of 14.3±2.3 nM. Moreover, p22 at a dose of 2.5 mg/kg, i.p. inhibited metastatic tumor growth in mice challenged with Lewis Lung carcinoma cells.

The A₆₁, and p22 polypeptides of the present invention are naturally occurring polypeptides as is shown by identification of A₆₁, and p22 in the serum of normal subjects as well as serum of cancer patients. The term “naturally occurring” as used herein is intended to mean that the substance referenced exists in nature and can be found in the body of a vertebrate. The substance may exist continuously or only intermittently in the body or only during particular physiologic or pathologic conditions in the body, The particular sample of a substance with is “naturally occurring” may not itself be made in the body of a vertebrate, but may be made by other means such as by chemical synthesis, recombinant methods or the like, so long as the substance is identical to the that made in the body of a vertebrate. By way of comparison, a man-made substance which has no corresponding identical substance made in the body of a vertebrate is not considered herein to be “naturally occurring”.

Also included within the scope of the present invention are polypeptides which are variants of A₆₁, and p22 polypeptides having sequences with conservative amino acid substitutions compared to the A₆₁ and p22 polypeptides. Conservative amino acid substitutions refer to the interchangeability of amino acids having similar chemical characteristics and/or having similar side chains. For example, a group of amino acids which are neutral and hydrophobic include alanine, valine, leucine, isoleucine, proline, tryptophan, phenylalanine and methionine; a group of amino acids which are neutral and polar include glycine, serine, threonine, tyrosine, cysteine, asparagine and glutamine; a group of amino acids which are basic include lysine, arginine and histidine; a group of amino acids which are acidic include aspartic acid and glutamic acid; a group of amino acids having aliphatic side chains is glycine, alanine, valine, leucine, and isoleucine; a group of amino acids having aliphatic-hydroxyl side chains is serine and threonine; a group of amino acids having amide-containing side chains is asparagine and glutamine; a group of amino acids having aromatic side chains is phenylalanine, tyrosine, and tryptophan; and a group of amino acids having sulfur-containing side chains is cysteine and methionine. Preferred conservative amino acids substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, lysine-arginine, alanine-valine, asparagine-glutamine, glutamic acid-aspartic acid, leucine-methionine, and glutamine-histidine.

The A₆₁, polypeptide of the present invention also includes glycosylated A₆₁. Glycoproteins are formed by attaching a carbohydrate side chain to an amino acid, most commonly, N-linked oligosaccharides in which the sugar is linked to the amino group of asparagine. Less common are O-linked oligosaccharides in which the sugar is linked to the hydroxyl group of serine or threonine. Glycosylation at any one or combination of these sites would increase the molecular weight of the molecule.

The A₆₁ and p22 polypeptides of the present invention isolated and purified polypeptides compared to their occurrence at very low levels and in a mixture of other substances in the body. An “isolated” substance or a “substantially pure” substance as used herein, particularly with reference to polypeptides or polynucleotides, is intended to mean that the substance is present, preferably, in an amount of at least about 50% on a molar basis of all macromolecular species present. More preferably, an isolated or substantially pure substance will comprise more than about 80% to about 90% o of all macromolecular species present in the composition. Most preferably, the substance is purified to essential homogeneity wherein contaminant species cannot be detected in the composition by conventional detection methods and the composition consists essentially of a single macromolecular species. Solvent species, small molecules (<500 Daltons), and elemental ion species are not considered macromolecular species.

Methods for preparing the A₆₁, and p22 polypeptides are also within the scope of the present invention. A₆₁ and p22 can be produced by cell-mediated methods or by cell-free methods.

A₆₁ can be prepared in vitro by plasmin autodigestion. Earlier work generated plasminogen fragments of the plasmin A-chain in a cell-free system of plasminogen uPA and the sulfydryl donor, N-acetyl-L-cysteine (see for example, Gately et al, Proc. Natl. Acad. Sci. U.S.A. 94:10868-10872, 1999; Fitzpatrick et al, Biochemistry 39:1021-1028, 2000). In contrast, the A₆₁ fragments of the present invention are generated as A-chain fragments by incubating plasminogen with uPA without any sulfhydryl donor. The reaction products can then be purified by L-lysine-Sephraose affinity and gel permeation chromatography. We have shown that the A₆₁ so produced is made up of two fragments which show an apparent mass of 61 and 64 kDa, respectively, on a Coomassie-stained, denaturing, reduced SDS-PAGE and an apparent mass of 50 kDa on Coomassie-stained denaturing, non-reduced SDS-PAGE. Typical recovery by this method is 51 mg A₆₁ from 100 mg plasminogen.

Cell-mediated systems can also be used to generate A₆₁. The cells are, preferably, mammalian cells, which can be derived from normal tissue or from cancerous tissue. Suitable mammalian cells are incubated overnight in media containing glu-plasminogen or lys-plasminogen, and cell-produced plasminogen fragments are produced. A₆₁ plasminogen fragments can be identified using reduced or non-reduced SDS-PAGE and Western blotting. We have found that HT1080 fibrosarcoma cells, bovine capillary endothelial cells and, to a lesser extent, HeLa cells and HUVEC cells were able to generate A₆₁. The A₆₁ plasminogen fragments so produced can be purified from the conditioned media by affinity chromatography.

The p22 plasminogen fragment can also be prepared in vitro. The method involves incubation of A₆₁ with plasmin and a reducing agent, such as dithiothreitol. Plasminogen fragments including p22 are thereby produced upon degradation of A₆₁. Subsequent purification of the reaction mixture using an L-lysine-Sepharose column results in the isolation of milligram quantities of p22.

Cell-mediated systems can also be used to generate p22. Preferably the cells are mammalian cells. Incubation of glu-plasminogen or lys-plasminogen with HT1080 human fibrosarcoma cells resulted in the generation of A₆₁ and p22 as well. The p22 fragment can be identified as a 22 kDa fragment in reduced SDS-PAGE and isolated using an L-lysine-Sepharose column.

A₆₁ polynucleotides and p22 polynucleotides are also within the scope of the present invention. Such polynucleotides encode A₆₁ polypeptides and p22 polypeptides, respectively. The human nucleic acid sequence of encoding human plasminogen precursor is shown in FIG. 2. The sequences encoding the two human A₆₁ isoforms are nucleic acids 343-1515 (SEQ ID NO:5) and nucleic acids 343-1524 (SEQ ID NO:6). The sequence encoding human p22 is nucleic acids 343-651 (SEQ ID NO:7). As would be readily appreciated by the skilled artisan, other nucleic acid sequences will encode the A₆₁ and p22 polypeptides as a result of code redundancy and these are also within the scope of the present invention.

The polynucleotides encoding A₆₁ polypeptides and the polynucleotides encoding p22 polypeptides also include sequences which encode human allelic variants of the polypeptides. In addition, the scope of the present invention includes polynucleotides encoding non-human mammalian polypeptides and non-mammalian vertebrate polypeptides.

Such polynucleotides in addition to the sequences shown in SEQ ID NOS:5-7 can be identified by virtue of their having at least a 90% identity with any one of SEQ ID NOS:5-7. By 90% sequence identity, it is meant that a sequence is of the same length and has at least 90% of the same bases as the reference sequence. Such sequences which are at least 90% identical to one of SEQ ID NOS:5-7 nevertheless, encode an A₆₁, or p22 polypeptide showing anti-angiogenic activity, preferably, endothelial cell anti-proliferative activity. A₆₁ polynucleotides encode the A₆₁ polypeptide of 391 and the A₆₁ polypeptide of 394, thus having 1173 consecutive nucleotides or 1182 consecutive nucleotides, respectively. The p22 polynucleotides encode p22 polypeptides of 103 contiguous amino acids thus having 309 consecutive nucleotides. Thus, in one embodiment, an A₆₁ polynucleotide can have 1173 consecutive nucleotides or 1182 consecutive nucleotides and also have at least 90% of the same bases as shown in SEQ ID NO:5 or SEQ ID NO:6, respectively. Similarly, in one embodiment, a p22 polynucleotide can have 309 consecutive nucleotides and at least 90% sequence identity with SEQ ID NO:7.

Nucleic acid sequences which specifically hybridize under stringent conditions with SEQ ID NOS:5, 6, or 7 are also within the scope of the present invention. Such polynucleotides, preferably, encode A₆₁ or p22 polypeptides and show anti-angiogenic activity. Stringent conditions or high stringency conditions allow one to distinguish a sequences which are not A₆₁, or p22 polynucleotides from sequences which are A₆₁ or p22 polynucleotides. Suitable stringent conditions can be selected by the skilled artisan on the basis of factors known to control the stringency of hybridization during hybridization and during the washing procedure, including temperature, ionic strength, length of time and concentration of formamide (See Sambrook et al., Molecular Cloning, 2nd Ed., 1989).

The present invention includes vectors comprising the A₆₁ or p22 polynucleotides as well as eukaryotic and prokaryotic cells comprising the vector. The cells can be mammalian cells. The mammalian cells can be, for example, human, murine, or bovine cells. The prokaryotic cells can be bacterial cells. The bacterial cells can be, for example E. coli cells. In addition, the vector can be, for example, a plasmid or a virus.

The present invention also includes the detection of A₆₁ polypeptides or p22 polypeptides in body fluids and tissues for the purpose of detection of diseases such as cancer or the angiogenic status of the diseases. As used herein, the term “detection” is intended to the determining of the presence of a disease in a patient, the distinguishing of the disease from other diseases, the estimation of prognosis in terms of probable outcome of the disease and prospect for recovery, the monitoring of the disease status or the recurrence of the disease, the determining of a preferred therapeutic regimen for the patient and the targeting of therapy. Such detection can involve any method known in the art for detecting proteins can be used including, but are not limited to immunodiffusion, immunoelectrophoresis, immunochemical methods, binder-ligand assays, immunohistochemical techniques, agglutination and complement assays. (for example see Basic and Clinical Immunology, Sites and Terr, eds., Appleton & Lange, Norwalk, Conn. pp. 217-262, 1991 which is incorporated by reference). Preferred are binder-ligand immunoassay methods including reacting antibodies with an epitope or epitopes of the A₆₁ polypeptides or p22 polypeptides and competitively displacing a labeled a A₆₁ or a p22 polypeptide or a derivative thereof.

As used herein, a derivative of an A₆₁ or a p22 polypeptide is intended to include a polypeptide in which certain amino acids have been deleted or replaced or changed to modified or unusual amino acids wherein the A₆₁ or a p22 derivative is biologically equivalent to A₆₁ or a p22 and wherein the polypeptide derivative cross-reacts with antibodies raised against the A₆₁ or a p22. By cross-reaction it is meant that an antibody reacts with an antigen other than the one that induced its formation.

Kits for measuring the levels of A₆₁ or a p22 in patient samples are also within the scope of the present invention. Such assay kits can be based any known protein assay method such as immunodiffusion, immunoelectrophoresis, immunochemical methods, binder-ligand assays, immunohistochemical techniques, agglutination and complement assays. Included in such kits are suitable reagents for conducting the assays.

Antibodies to A₆₁ and p22 are also within the scope of the present invention. Such antibodies can be polyclonal or monoclonal antibodies. Polyclonal antibodies can be prepared by immunizing rabbits or other animals by injecting antigen followed by subsequent boosts at appropriate intervals. The animals are bled and sera assayed against purified A₆₁ or p22 polypeptide. When using avian species, e.g. chicken, turkey and the like, the antibody can be isolated from the yolk of the egg. Monoclonal antibodies can prepared after the method of Milstein and Kohler by fusing splenocytes from immunized mice with continuously replicating tumor cells such as myeloma or lymphoma cells. (Milstein and Kohler Nature 256:495-497, 1975; Gulfre and Milstein, Methods in Enzymology: Immunochemical Techniques 73:1-46, Langone and Banatis eds., Academic Press, 1981 which are incorporated by reference). The hybridoma cells so formed are then cloned by limiting dilution methods and supernates assayed for antibody production by ELISA, RIA or bioassay.

Specific antibodies, either polyclonal or monoclonal, to the A₆₁ or p22 can be produced by any suitable method known in the art as discussed above. For example, murine or human monoclonal antibodies can be produced by hybridoma technology or, alternatively, the A₆₁ or p22 polypeptide, or an immunologically active fragment thereof, or an anti-idiotypic antibody, or fragment thereof can be administered to an animal to elicit the production of antibodies capable of recognizing and binding to A₆₁ or p22 polypeptides. Such antibodies can be from any class of antibodies including, but not limited to IgG, IgA, IgM, IgD, and IgE or in the case of avian species, IgY and from any subclass of antibodies.

The present invention also includes methods of treating or preventing angiogenic diseases and conditions. Such angiogenic diseases and conditions include, for example, solid tumors; blood born tumors such as leukemias; tumor metastasis; benign tumors, such as hemangiomas, acoustic neuromas, neurofibromas, trachomas, and pyogenic granulomas; rheumatoid arthritis; psoriasis; ocular angiogenic diseases, such as, diabetic retinopathy, retinopathy of prematurity, macular degeneration, corneal graft rejection, neovascular glaucoma, retrolental fibroplasia, rubeosis; Osler-Webber Syndrome; myocardial angiogenesis; plaque neovascularization; telangiectasia; hemophiliac joints; angiofibroma; wound granulation; intestinal adhesions; Crohn's disease; atherosclerosis; scleroderma; and hypertrophic scars, i.e., keloids.

The method of treatment involves administration to a patient an angiogenesis-inhibiting amount of a A₆₁ and/or p22 to the mammal. The method is applicable to any disease or condition involving unwanted angiogenesis, in particular the growth of tumors in cancer. The mammal is preferably a human and the A₆₁, and/or p22 are preferably human polypeptides. The A₆₁ and/or p22 can also be administered in combination with other agents to treat the particular disease such as, for example, other anti-cancer agents for treating cancer.

Cytotoxic agents can also be linked to A₆₁, or to p22 to provide a composition which can be used to target cancer cells. Such cytotoxic agents include ricin, deoxyribonuclease, diphtheria toxin, pseudomonal exotoxin, ribonuclease and the like.

Gene therapy approaches are also within the scope of the present invention. Such can include administration of the polynucleotides of the present invention or compositions of the polynucleotides in a vector system such as a noninfectious viral vector to deliver the polynucleotide fragment to the target cells of the patient. Chemical approaches can also be used in the administration of the polynucleotides, including incorporation into liposomes as well as conjugating with lipofectins or cytofectins.

Also included in the present invention are ex vivo approaches in which the polynucleotides of the present invention are administered to cells obtained from the patient, followed by administration or implantation of the cells into the patient. A₆₁ or p22 can also be administered to vascular endothelial cells to prevent proliferation. The cells can be in vitro or in vivo. The method comprises administering to the cells A₆₁ or p22 or a combination thereof in an amount suitable for inhibiting endothelial cell proliferation.

The present invention also includes therapeutic or pharmaceutical compositions of A₆₁ or p22 polypeptides or polynucleotides. The compositions comprise an effective amount for treating patients with angiogenic diseases or conditions in pharmaceutically acceptable formulations. These formulations can be administered by standard routes of administration such as, for example, by topical, transdermal, intraperitoneal, intracranial, intracerebroventricular, intracerebral, intravaginal, intrauterine, oral, rectal, intravenous, intraspinal, subcutaneous or intramuscular routes. The A₆₁ or p22 molecules can also be linked or conjugated with agents that provide desirable pharmaceutical or pharmacodynamic properties. For example A₆₁ or p22 can be conjugated polyethylene glycol to provide more desirable pharmacokinetic parameters. Delivery methods known in the art such as osmotic minipumps may also be used to provide a targeted delivery at the site of a tumor. Parenteral administration can be either rapid as by injection or over a period of time as by slow infusion or administration of slow release formulation.

The compositions of the present invention are usually employed in the form of pharmaceutical preparations. Such preparations are made in a manner well known in the pharmaceutical art. One preferred preparation utilizes a vehicle of physiological saline solution, but it is contemplated that other pharmaceutically acceptable carriers such as physiological concentrations of other non-toxic salts, five percent aqueous glucose solution, sterile water or the like may also be used. It may also be desirable that a suitable buffer be present in the composition. Such solutions can, if desired, be lyophilized and stored in a sterile ampoule ready for reconstitution by the addition of sterile water for ready injection. The primary solvent can be aqueous or alternatively non-aqueous. The compositions of the present invention can also be incorporated into a solid or semi-solid biologically compatible matrix such as a polymer which can be implanted into tissues requiring treatment. Such compositions can be implanted to allow for targeting at a particular tumor site or to provide slow release, for example, at the site of a tumor or implanted so that the angiostatin is slowly released systemically.

The carrier can include pharmaceutically-acceptable excipients for modifying or maintaining the pH, osmolarity, viscosity, clarity, color, sterility, stability, rate of dissolution, or odor of the formulation. Similarly, the carrier may contain still other pharmaceutically-acceptable excipients for modifying or maintaining release or absorption or penetration across the blood-brain barrier. Such excipients are those substances usually and customarily employed to formulate dosages for parenteral administration in either unit dosage or multi-dose form or for direct infusion into the cerebrospinal fluid by continuous or periodic infusion.

Dose administration can be repeated depending upon the pharmacokinetic parameters of the dosage formulation and the route of administration used.

It is also contemplated that certain formulations containing A₆₁ or p22 can be administered orally. Such formulations are preferably encapsulated and formulated with suitable carriers in solid dosage forms. Some examples of suitable carriers, excipients, and diluents include lactose, dextrose, sucrose, sorbitol, mannitol, starches, gum acacia, calcium phosphate, alginates, calcium silicate, microcrystalline cellulose, polyvinylpyrrolidone, cellulose, gelatin, syrup, methyl cellulose, methyl- and propylhydroxybenzoates, talc, magnesium, stearate, water, mineral oil, and the like. The formulations can additionally include lubricating agents, wetting agents, emulsifying and suspending agents, preserving agents, sweetening agents or flavoring agents. The compositions may be formulated so as to provide rapid, sustained, or delayed release of the active ingredients after administration to the patient by employing procedures well known in the art. The formulations can also contain substances that diminish proteolytic degradation and promote absorption such as, for example, surface active agents.

The specific dose is calculated according to the approximate body weight or body surface area of the patient or the volume of body space to be occupied. The dose will also be calculated dependent upon the particular route of administration selected. Further refinement of the calculations necessary to determine the appropriate dosage for treatment is routinely made by those of ordinary skill in the art. Such calculations can be made without undue experimentation by one skilled in the art in light of the activity disclosed herein in assay preparations of target cells. Exact dosages are determined in conjunction with standard dose-response studies. It will be understood that the amount of the composition actually administered will be determined by a practitioner, in the light of the relevant circumstances including the condition or conditions to be treated, the choice of composition to be administered, the age, weight, and response of the individual patient, the severity of the patient's symptoms, and the chosen route of administration.

Preferred embodiments of the invention are described in the following examples. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the specification or practice of the invention as disclosed herein. It is intended that the specification, together with the examples, be considered exemplary only, with the scope and spirit of the invention being indicated by the claims which follow the examples.

EXAMPLE 1

This example illustrates the generation and identification of A₆₁ lasmin(ogen) fragments produced by plasmin autodigestion using a cell-free system. Previous reports (Gately et al. (1997) Proc. Natl. Acad. Sci. U.S.A. 94: 10868-10872; U.S. Pat. No. 5,801,012 to Soff et al.) showed that a kringle1-4-containing plasminogen cleavage product of 50 kDa (non-reduced SDS-PAGE) was generated in a cell-free system consisting of plasminogen, u-plasminogen activator, and the sulfhydryl donor N-acetyl-L-cysteine. It was also reported that the formation of the kringle1-4 plasminogen A-chain fragment was absolutely dependent on the presence of a sulfhydryl donor such as N-acetyl-L-cysteine.

In a reinvestigation of the dependency on the presence of a sulfhydryl donor to generate a plasminogen fragment comprising kringles 1-4 by plasmin autodigestion, the present inventors unexpectedly observed that plasmin(ogen) autodigestion in the absence of a sulfhydryl donor generated of novel molecular species. These species, comprising a major band of 61 kDa and a minor band of 64 kDa were collectively named “A₆₁” to avoid confusion with the plasminogen fragment angiostatin.

To generate A₆₁, [Glu]plasminogen (40 μM) was incubated overnight at 37° C. (in the absence of a sulfhydryl donor) in a buffer containing 50 mM Tris-HCl (pH 9.0), 20 mM L-lysine, 100 mM NaCl, 1 mM EDTA, and 0.17 μM two-chain u-plasminogen activator (urokinase), thereby forming a mixture including the A₆₁. Following the incubation, the mixture was diluted 4-fold with a buffer comprising 20 mM Hepes (pH 7.4) and 140 mM NaCl, adjusted to 1 mM diisopropylfluorophosphate (DIFP), and applied to an L-lysine-Sepharose affinity chromatography column (Pharmacia) previously equilibrated with equilibration buffer comprising 20 mM Hepes (pH 7.4) and 140 mM NaCl. After a 5-column volume wash with equilibration buffer, the column was subjected to a linear gradient of 0-125 mM ε-amino-n-caproic acid, and a single protein peak (as observed by monitoring sample absorbance of 280 nm ultraviolet light) was eluted, pooled, and concentrated by ultrafiltration. Application of this protein peak to a Sephacryl S-100 column (Pharmacia) previously equilibrated with equilibration buffer resulted in the elution of a single protein peak that was collected in fractions. The fractions were pooled, then divided into aliquots which were stored frozen at −80° C. until further use. Samples from the protein peak were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE; Laemmli, U.K. (1970) Nature 227: 680-685).

For Western blotting, proteins were transferred from gels to 0.45-μm pore size nitrocellulose membranes using a Bio-Rad transblot apparatus at 4° C. for 1 h for mini-gels or overnight for larger gels. The membranes were then blocked in TPBS (wherein TPBS is phosphate-buffered saline containing 137 mM NaCl, 8 mM Na₂HPO₄, 1.4 mM KH₂PO₄, 2.7 mM KCl (pH 8.0), and 0.1% Tween 20 detergent) containing 5% skim milk at room temperature for 1 h and then incubated with primary antibody in TPBS containing 1% skim milk at 4° C. overnight. The following dilutions of primary antibody were used: 1:5000 dilution of 1 mg/ml monoclonal anti-human plasminogen kringle 1-3 antibody; 1:500 dilution of 0.1 mg/ml monoclonal anti-human angiostatin antibody (GF-47); 1:500 dilution of polyclonal anti-mouse angiostatin antibody. Blots were then washed with TPBS at least 6 times (10 minutes each) at room temperature and then incubated in 1:1000 dilution of anti-mouse or anti-rabbit horseradish peroxidase-conjugated secondary antibody in TPBS containing 1% skim milk at 37° C. for 1 hour. Membranes were then washed with TPBS at least six times (10 minutes each), developed with the Supersignal reagent (Pierce), and visualized by chemiluminescence.

FIG. 3 illustrates the generation and isolation of A₆₁ produced in a cell-free system. To produce, [Glu]plasminogen (40 μM) was incubated in buffer comprising 50 mM Tris-HCl (pH 9.0), 20 mM L-lysine, 100 mM NaCl, 1 MM EDTA, and 0.17 μM two-chain u-plasminogen activator (lane 1). The reaction mixture was incubated at 37° C. overnight (lane 2). The mixture was diluted 4-fold with equilibration buffer adjusted to 1 mM diisopropylfluorophosphate, and applied to a lysine-Sepharose column previously equilibrated equilibration buffer. After a 5-column volume wash with equilibration buffer, the column was subjected to a linear gradient of 0-125 mM ε-amino-n-caproic acid. Fractions comprising the 61- and 64 kDa plasminogen fragments were collected and pooled (lane 3), concentrated by ultrafiltration, and applied to a Sephacryl gel permeation (Gel Perm) chromatography column previously equilibrated with equilibration buffer. The protein peak was then pooled (lane 4). Aliquots of pooled fractions were analyzed by reduced (A) and non-reduced SDS-PAGE (B) and stained with Coomassie Blue. Alternatively, aliquots were analyzed by non-reduced SDS-PAGE, transferred to a nitrocellulose membrane, and analyzed by Western blotting (below) using a monoclonal antibody against human plasminogen kringles 1-3 as the primary antibody (FIG. 3C).

Comparison of stained bands with molecular size standards on a gel run under reducing conditions established that the protein peak comprised an isolated doublet comprising major and minor proteins of M_(r) 61,000 and 64,000, respectively Therefore, these A-chain fragments were collectively named A₆₁. The concentration of A₆₁ was determined using an ε_(1%,280nm) 13.6 and a molecular mass of 61 KDa. Recovery was about 51 mg of A₆₁, from 100 mg of [Glu]plasminogen. A₆₁ was also formed with a comparable yield when [Lys]plasminogen was substituted for [Glu]plasminogen.

To investigate the mechanism of A₆₁, production, the time course of generation of A₆₁ from plasminogen and u-plasminogen activator was examined using SDS-PAGE under reducing and non-reducing conditions. For these experiments, [Glu]plasminogen (8.7 μM) was incubated at 37° C. in a buffer containing 50 mM Tris (pH 9.0), 100 mM NaCl, 1 mM EDTA, and 20 mM L-lysine. Samples were removed at time intervals as indicated in FIG. 4, and the reaction stopped by dilution and heating of the samples in SDS-PAGE sample buffer (with or without reducing agent), then subjected to SDS-PAGE under reducing or non-reducing conditions.

FIG. 4 shows a time course analysis of plasminogen cleavage to A₆₁. [Glu]plasminogen (8.7 μM), incubated as described above. The reaction was initiated by addition of 39 nM u-plasminogen activator. Aliquots of the reaction were removed at the indicated times, subjected to reduced (FIG. 4A) and non-reduced-SDS-PAGE (FIG. 4B), and stained with Coomassie Blue. Pm_(H) indicates plasmin heavy chain; Pm_(L) indicates plasmin light chain.

The data shown in FIG. 4 indicate that [Glu]plasminogen (8.7 μM) is completely converted to plasmin by about 5 minutes after initiation of the reaction by addition of u-plasminogen activator (39 nM). However, at this point in the reaction, A₆₁ is not observed. After the reaction progresses for about 1 h, degradation of the plasmin heavy and light chains becomes apparent. Analysis of reaction products by SDS-PAGE shows that by about 2-4 hours after initiation of the reaction, A₆₁ is apparent, exhibiting M_(r)'s of about 61,000 and 64,000 on gels run under reducing conditions and an M_(r) of about 50,000 in gels run under non-reducing conditions.

Separate experiments demonstrated that a recombinant human plasminogen (S741C) that is catalytically inactive when converted to plasmin was not converted to A₆₁ (Horrevoets, A. J. G. et al. (1997) Journal of Biological Chemistry 272: 2176-2182). While not wishing to be bound by theory, these results indicate that plasminogen is cleaved by u-plasminogen activator to form plasmin which then undergoes autodigestion resulting in the formation of A₆₁. Because A₆₁ can be generated by plasmin autoproteolysis, plasmin obtained by methods other than u-plasminogen activator cleavage of plasminogen, for example converting plasminogen to plasmin using other plasminogen activators such as t-plasminogen activator or streptokinase, or generating plasmin using recombinant DNA methods, can substitute to generate plasmin that can undergo autoproteolysis to form A₆₁.

The concept that plasmin is capable of autodigestion in the absence of sulfhydryl donors is not novel. Other laboratories have shown that plasmin autodigestion involves a bimolecular reaction in which both heavy and light chains are proteolyzed (Walther, P. J., et al., (1974) J. Biol. Chem. 249, 1173-1181; Grimard, M. (1976) Biochimie (Paris) 58, 1409-1412; Gaffney, P. J., et al., (1977) Haemostasis 6, 72-88; Reddy, K. N., and Wagner, C. J. (1980) Biochem. Biophys. Res. Commun. 92, 1016-1022; Jespersen, J., et al., (1986) Thromb. Res. 41, 395-404; Wu, H. L., et al., (1987) Proc. Natl. Acad. Sci. U.S. A. 84, 8793-8795; Shi, G. Y., and Wu, H. L. (1988) Thromb. Res. 51, 355-364). Two autodigestive processes involving human plasmin have been reported by Wu and co-workers (Shi, G. Y., and Wu, H. L. (1988) Thromb. Res. 51, 355-364). In a slightly acidic solution the light chain was found to be cleaved faster than the heavy chain of plasmin. The cleavage of the light chain correlated with loss of plasmin activity. Both the heavy chain and the light chain were cleaved at pH levels between 6.5 and 11.0. On the other hand, alkaline pH favored the cleavage of the heavy chain. A cleaved heavy chain of molecular weight 50,000 (reduced SDS-PAGE) or 58,000 was observed (Shi, G. Y., and Wu, H. L. (1988) Thromb. Res. 51, 355-364). The C terminus of the M_(r) 58,000 fragment was shown to be Arg⁵³⁰. Based on these data it has been theorized that because of their proximity in the plasminogen structure, the disulfide bonds between Cys⁵¹² and Cys⁵³⁶ and between Cys⁴⁶² and Cys⁵⁴¹ could be split by hydroxyl ions. Without wishing to be bound by theory, the cleavage of the disulfide bonds between Cys⁴⁶² and Cys⁵⁴¹ could explain how plasmin autodigestion results in the formation of A₆₁, in the absence of sulfhydryl donors or a plasmin reductase.

EXAMPLE 2

This example illustrates the generation and identification of A₆₁ plasmin(ogen) fragments produced by contacting plasminogen with cells in vitro.

The ability of many cells to bind plasminogen and convert the plasminogen to plasmin at the cell surface has been well established. Whereas plasminogen can be converted to plasmin at the cell surface by the action of plasminogen activators such as u-plasminogen activator, it has been recently shown that other plasminogen fragments are also produced at the cell surface (Gately, S., et al. (1996) Cancer Res. 56: 4887-4890; O'Mahony, C. A., et al. (1998) J. Surg. Res. 77: 55-58; Westphal, J. R., et al. (2000) Int. J. Cancer 86: 760-767). To compare the plasminogen fragments produced on the cell surface with A₆₁, human HT1080 fibrosarcoma cells were incubated with [Glu]plasminogen, and the cell-produced plasminogen fragments were analyzed by reduced or non-reduced SDS-PAGE and Western blotting.

To generate A₆₁ with the aid of cells, human HT1080 or bovine capillary endothelial (BCE) cells were grown in Dulbecco's Modified Eagle Medium (DMEM; JRH Biosciences or GIBCO-BRL) supplemented with 10% heat-inactivated fetal calf serum, 2 mM L-glutamine, 10 units/ml penicillin G and 10 μM streptomycin sulfate in T75 tissue culture flasks at 37° C. Approximately 1×10⁵ cells in 1 ml were added to each well of 24-well tissue culture plates and incubated at 37° C. for approximately 24 hr, wherein the cells formed monolayers. The cells monolayers were washed three times with phosphate buffered saline (PBS; 137 mM NaCl, 8 mM Na₂ HPO4, 1.4 mM KH₂PO₄, 2.7 mM KCl, pH 8.0), and 0.5 to 8 μM [Glu]-plasminogen in DMEM was then added to each well, thereby forming a mixture including the A₆₁. Culture medium (about 100 ml) was collected after overnight incubation and centrifuged at about 2000×g at 4° C. for about 30 min to remove cell debris. Supernatants from the centrifuged samples were then applied to an L-lysine-Sepharose affinity chromatography column previously equilibrated with equilibration buffer. After a 5-column volume wash with equilibration buffer, the column was subjected to a linear gradient of 0-125 mM ε-amino-n-caproic acid. Fraction samples were subjected to SDS-PAGE conducted with or without reducing agent, and analyzed by Western blotting (below) using a monoclonal antibody against human plasminogen kringles 1-3 as the primary antibody. The peak fractions containing A₆₁ were pooled and concentrated. The proteins were desalted using a Sephadex PD-10 column (Amersham Pharmacia Biotech) into endotoxin-free PBS (Life Technologies, Inc.), filtered, and frozen in small aliquots at 80° C. SDS-PAGE and Western blot analysis indicates that some (but not all) mammalian cell types are capable of generating A61 from plasmin(ogen).

FIG. 13 shows a comparison of A₆₁ with cell-generated plasminogen fragments. For these experiments, HT1080 cells were incubated with DMEM containing the indicated concentrations of [Glu]plasminogen. After an overnight incubation, the media were analyzed by 15% reduced (FIG. 13A) and non-reduced (FIG. 13B) SDS-PAGE followed by Western blotting with monoclonal anti-human plasminogen kringle 1-3 antibody: [Glu]plasminogen standard (lane 1); [Glu]plasminogen (8 μM) after overnight incubation in the absence of cells (lane 2). The HT1080 cells were incubated with the following concentrations of [Glu]plasminogen; 0.5 μM (lane 3); 1 AM (lane 4); 2 μM (lane 5); 4 μM (lane 6); 8 μM [Glu]plasminogen (lane 7); A₆₁ standard (lane 8).

As shown in FIG. 13C, Human [Glu]plasminogen (8 μM) in DMEM was incubated overnight with a variety of cell lines. After an overnight incubation the media were subjected to 12.5% reduced SDS-PAGE followed by Western blotting with the monoclonal anti-human plasminogen kringle 1-3 antibody. The plasminogen standard (lane 1) and A₆₁ standard (lane 2) are also shown. Plasmin(ogen) and digestion products resulting from plasmin(ogen)/cell contact are shown by Western blot for the following cell lines: HT1080 cells (lane 3), HeLa cells (lane 4), BCE cells (lane 5), or HUVECs (lane 6).

The results demonstrate that both HT 1080 and BCE cells convert plasmin(ogen) to a molecule indistinguishable by Western blot analysis from A₆₁ generated using the cell-free system. First, it was found that cultured cells produced a plasminogen fragment of similar M_(r) to that of A₆₁ which indicates that the predominant cell-produced A-chain fragment was composed of at least four intact kringles. Second, the observation that BCE cells produced an A₆₁-like protein indicates that the formation of A-chain fragments is not restricted to cancer cells. Furthermore, N-terminal sequencing of the A₆₁-like plasminogen fragment produced by the HT1080 or BCE cells established that the N terminus of the cell-produced A₆₁ is identical to A₆₁ produced using the cell-free system.

To demonstrate the inhibitory effect of A₆₁ generated by cell/plasminogen contact on endothelial cell proliferation in vitro, a growth inhibition assay was as described in Example 5 below. For these experiments, Human [Glu]plasminogen (2.7 μM) was incubated with HT1080 or BCE cells overnight (FIG. 13D). The A61 was purified from the culture media of the HT1080 (closed circles) and BCE cells (open circles) by affinity chromatography with L-lysine-Sepharose. Various concentrations of the cell-generated A61 were added to BCE cells, and the extent of inhibition of BCE cell growth was determined as indicated in Example 5. The observation that the A₆₁-like protein produced by HT1080 or BCE cells possessed potent anti-angiogenic activity further supports our notion that normal unstimulated cells can produce anti-angiogenic plasminogen fragments.

Because the molecular and biological properties of the plasmin(ogen) fragments produced by using the cell-free method or by contacting plasminogen with BCE or HT1080 cells appear identical, it is believed that these methods can all be used to generate A₆₁.

EXAMPLE 3

This example demonstrates the presence of A₆₁, in sera of healthy and diseased mammals, including mice.

It was originally proposed that the angiostatin fragment plasminogen of M_(r) 38,000-43,000 on SDS-PAGE under reducing conditions was present in the urine and serum of mice bearing Lewis lung carcinoma tumors, but not in the serum of normal mice or tumor-resected mice (O'Reilly, M. S., et al., (1994) Cell 79: 315-328). Accordingly, serum was examined for the presence of an A₆₁-like fragment. In these experiments, 200 μl of mouse or human serum was incubated at room temperature for 30 min with 50 μl of a 1:1 suspension of L-lysine-Sepharose matrix (previously equilibrated with equilibration buffer). The matrix was subsequently washed with 5 volumes of the same buffer. The bound proteins were eluted by boiling the resin with SDS-PAGE sample buffer, and 20 μl of each sample was subjected to non-reduced SDS-PAGE and Western blotting.

FIG. 5 presents a comparison of A₆₁ with plasminogen fragments present in mouse sera. Sera collected from mice were incubated with 50 μl of L-lysine-Sepharose (equilibrated in 20 mM Hepes, (pH 7.4), 140 mM NaCl) for 30 min at room temperature. The matrix was washed with 5 volumes of equilibration buffer, boiled with SDS-PAGE sample buffer, and subjected to non-reduced SDS-PAGE. Western blotting was performed with rabbit anti-mouse angiostatin antibody (FIG. 5A) or monoclonal anti-human plasminogen kringle 1-3 antibody (figure SB). The lanes in FIG. 5A are as follows:, control mouse serum, (1 and 2); mouse serum from two individual mice with 14-day old Lewis Lung Carcinoma tumor (see Example 5 below), (3 and 4); mouse serum from two individual mice 14 days after tumor resection, (5 and 6). The lanes in FIG. 5B are as follows: A₆₁ standard (1); mouse with 14-day old tumor (2); 3 days after tumor resection (3); 6 days after tumor resection (4); 9 days after tumor resection (5); 12 days after tumor resection (6); 15 days after tumor resection (7).

The results in A were consistent with test groups consisting of 21 normal mice, 9 tumor-bearing mice, and 29 tumor-resected mice.

As shown in FIG. 6, the Western blots presented in FIG. 5A and FIG. 5B demonstrate that the serum from normal, tumor-bearing, and tumor-resected mice all had detectable levels of an A₆₁-like plasminogen fragment. In these experiments, the blots were probed with human monoclonal anti-human plasminogen kringle 1-3 antibody (FIG. 6, a′) or rabbit anti-mouse angiostatin antibody (FIG. 6, b′). The mouse plasminogen fragment labeled by these antibodies ran with an M_(r) of about 50,000 on SDS-PAGE under non-reducing conditions and was also detectable with a anti-human kringle 1-3 monoclonal antibody (FIG. 5C, a′). Unlike angiostatin, the A₆₁-like protein was present in both normal sera and sera from tumor-bearing animals, and no appreciable change in the concentration of the A₆₁-like plasminogen fragment was observed from 3 to 15 days after tumor resection (FIG. 5B, and FIG. 6, b′).

The presence of an A₆₁-like protein in the sera of healthy and tumor-bearing mice led to an investigation of the presence of an A₆₁-like protein in human subjects. FIG. 7 presents a comparison of A₆₁ with plasminogen fragments present in human sera. Frozen human sera from normal volunteers (A) or cancer patients (B) were thawed and then incubated with 50 μl of lysine-Sepharose (equilibrated in 20 mM Hepes (pH 7.4), 140 mM NaCl) for 30 min at room temperature. The matrix was washed with 5 volumes of equilibration buffer, boiled with SDS-PAGE sample buffer, and subjected to non-reduced SDS-PAGE. Western blotting was performed with monoclonal anti-human angiostatin antibody. A, angiostatin (Calbiochem) standard (250 ng) (lane 1); A₆₁ standard (250 ng) (lane 2); serum from healthy laboratory volunteers (lanes 3-11). B, angiostatin (Calbiochem) standard (250 ng) (lane 1); A₆₁ standard (250 ng) (lane 2); testicular cancer (lane 3); head and neck cancer (lanes 4 and 5); testicular cancer (lanes 6-8); head and neck cancer (lanes 9 and 10).

As shown in FIG. 7, unlike angiostatin, the A₆₁-like plasminogen fragment was present in the serum of every individual examined. Because of its presence in the sera of healthy and diseased mice and humans, it is concluded that unlike angiostatin, an A₆₁-like plasminogen fragment is a normal component of mammalian serum, and that this fragment can be isolated using the techniques described herein. Without wishing to be bound by theory, it appears that the A₆₁-like molecule is produced in the serum simply as a result of plasmin autodigestion. Although the biological activity of serum-derived A₆₁-like molecule has not been tested, this serum component can be further isolated using standard techniques of chromatography, such as ligand affinity, gel filtration, ion exchange, reverse-phase, and hydrophobic interaction chromatography.

EXAMPLE 4

This example discloses biochemical and biophysical properties of A₆₁.

Because large quantities of A₆₁ were easily generated, N-terminal sequence and C-terminal sequence of A61 could be determined. Terminal sequences were determined by commercial facilities using standard techniques. N-terminal sequence was determined by Edman degradation, and C-terminal sequences were determined using a Hewlett-Packard HP G1000A C-terminal protein sequencer and an Applied Biosystems 477C Procise C C-terminal sequencer. Consistent results were obtained from the sequencers. The Hewlett-Packard HP G1000A C-terminal protein sequencer utilized chemistry version 2.0 using diphenylphosphorylisothiocyanate as the activating agent (Bailey, J. M. et al. (1992) Protein Sci. 1: 1622-1633) and a modified cleavage system using lithium ethiolate as the cleavage agent (U.S. Pat. No. 5,986,071 to Graham et al.). An Applied Biosystems 477C Procise C C-terminal sequencer used standard chemistry as described (Boyd, V. L. (1992) Analytical Biochemistry 206: 344-352).

The N-terminal sequence of the A₆₁ was determined to be Lys⁷⁸-Glu⁸³. Major and minor C-terminal sequences were identified as Lys⁴⁶⁸-Gly⁴⁶⁵ and Arg^(47l)-Gly⁴⁶⁷, respectively (Table I). Thus, by comparing N- and C-terminal sequences to the known sequence of plasminogen, it was established that the autoproteolytic cleavage sites of plasmin were Lys⁷⁷-Lys⁷⁸, Lys⁴⁶⁸-Gly⁴⁶⁹, and Arg⁴⁷¹-Gly⁴⁷². Therefore, the major species of A₆₁ has the primary amino acid sequence of Lys⁷⁸-Lys⁴⁶⁸, whereas the minor species is Lys⁷⁸-Arg⁴⁷¹. The average molecular mass predicted from this amino acid sequence is 44.1 kDa.

TABLE I^(a) Amino- and Carboxyl-Terminal Sequence of Human A₆₁ Plasminogen G₄₆₅ N₄₆₆ G₄₆₇ K₄₆₈ G₄₆₉ Y₄₇₀ R₄₇₁ A₆₁ C- G K G Y R Sequence A A₆₁ C- G N G K Sequence B Plasminogen K₇₈ V₇₉ Y₈₀ L₈₁ S₈₂ E₈₃ A₆₁ N- K V Y L X E Sequence ^(a)Human A₆₁ was generated from human plasminogen and uPA in the cell-free system as described in the text. The molar ratio of A₆₁ C-sequence A and B was 2:5.

N- and C-terminal sequencing has allowed the precise elucidation of the primary structure of A₆₁ as comprising the amino acid sequence Lys⁷⁸-Lys⁴⁶⁸. Other A-chain fragments have been reported, but the absence of C-terminal sequencing has made the exact identification of these fragments difficult. Plasminogen is cleaved by a variety of proteinases including metalloelastase, matrix metalloproteinases, and serine proteinases to generate kringle 1-3, kringle 1-4, and kringle 1-4.5 fragments (Table II). Typically these A-chain fragments terminate at amino acid residues in the linker regions between the K3 and K4 (C-terminal Val338/354 residues for kringle 1-3), the linker regions between kringle 4 and kringle 5 (C-terminal Ala440 or Pro446/447 for kringle 1-4), or within residues of kringle 5 (C-terminal Arg530 for kringle 1-4.5). Therefore, A₆₁ is a novel A-chain fragment that belongs to the kringle 1-4.5 class of A-chain fragments except that it contains only 7 residues of kringle 5.

TABLE II Comparison of various A-chain fragments Method of MW Plasminogen Structure (kDa) Kringles IC₅₀ (nM) Cleavage Reference Y80-A440 51-54 K1-4 70 Elastase (Takada et al., 1988) Y80-V338/354 41-44 K1-3 135 Elastase (Takada et al., 1988) N60-P447 55 K1-4 MMP-3 (Lijnen et al., 1998) K78-P447 58 K1-4 MMP-7 (Patterson and Sang, 1997) K78-P446 58 K1-4 MMP-9 (Patterson and Sang, 1997) K78-K468 61 K1-4 + 7rK5 35 Autodigestion (Kassam et al., 2001) K78-R530 (?) 66, 60, 57 K1-4 + 69rK5 Plasmin reductase (Stathakis et al., 1999) and serine protease K78-?  50* K1-4 (?) 300 Reduction and (Gately et al., 1997) Autodigestion K77-? 42, 48, 50* K1-4 (?) Autodigestion (Falcone et al., 1998) K78-R530 55 K1-4 + 69rK5 0.050 Autodigestion at pH 11 (Cao et al., 1999) L74-L451 49, 51* K1-4 17 Recombinant (Sim et al., 1997) L74-P349  36* K1-3 Recombinant (MacDonald et al., 1999) unknown 38 K1-(?) MME (Dong et al., 1997)

Abbreviations in Table 2 are as follows: K, kringle; r, amino acid residues; MME, macrophage metalloelastase. Numbering in the Table is based on the sequence of human plasminogen (791 residues) excluding the 19 amino acid signal peptide that ends at Met-19 and beginning at Glu-1 (Forsgren et al., 1987). The molecular weights were determined by reduced SDS-PAGE or non-reduced SDS-PAGE (*). The angiostatin activity of the A-chain fragments, the IC₅₀, was determined as the concentration of A-chain fragment required to half-maximally inhibit the proliferation of bovine capillary endothelial cells. To allow a direct comparison of the angiostatin activity, results were pooled from several reports (Cao et al., 1996). The symbol (?) indicates proposed structures that were not confirmed by C-terminal sequencing.

To investigate the possibility of post-translational modifications of A₆₁ (in addition to the proteolytic cleavages), the molecular mass of A₆₁ was measured by mass spectrometry by the technique of matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. Mass spectra were obtained using a Voyager DE-STR (PE Biosystems) MALDI time-of-flight mass spectrometer. For this analysis, samples of A₆₁ were individually loaded onto pre-equilibrated ZipTips (Millipore Corp.) in four 4-μl increments, for de-salting and pre-concentration. The samples were each eluted from their Tip with 2 μl of recrystallized Sinapinic (3,5-dimethoxy-4-hydroxycinnamic acid) matrix solution, 1 μl at a time, onto a 100-well stainless steel sample slide. After introduction of the slide into the mass spectrometer, a linear MALDI method was employed to obtain sample spectra. The method employed a 20-kV accelerating voltage, a nitrogen laser (337 nm, UV wavelength), and a 350-ns extraction delay time. Each data set was noise-filtered, smoothed twice, entroided, and de-isotoped to remove the isotope contributions from the centroided-isoform spectrum. Mass spectrometry of A₆₁ revealed a broad cluster of features of about 1-kDa width. The dominant species in the cluster smoothed into a molecular mass of 46,616 daltons when the cluster was centroided and de-isotoped. This measured molecular mass is significantly greater than the average molecular mass of approximately 44.1 kDa predicted from the amino acid sequence. The comparison of the 46.6-kDa fragment of A₆₁ derived from mass spectrometric analysis with the 44.5-kDa fragment derived from the amino acid sequence of the protein suggests that like the parent molecule, plasminogen, A₆₁ is glycosylated (Hayes, M. L., and Castellino, F. J. (1979) J. Biol. Chem. 254: 8772-8776; Hayes, M. L., and Castellino, F. J. (1979) J. Biol. Chem. 254: 8777-8780). Plasminogen contains N-linked carbohydrate residues on kringle 3 and two O-linked carbohydrate on Ser249 and Thr346 of the kringle 2-kringle 3 linker and kringle 3-kringle 4 linker, respectively. The role of these glycosylations is unclear, but studies of A-chain fragment glycoforms have suggested that the extent of glycosylation may affect the biological activity or half-life of the protein in circulation (Pirie-Shepherd, S. R. (1999) J. Lab. Clin. Med. 134, 553-560).

A comparison of the amino acid sequence of A₆₁ with other A-chain fragments is presented in Table II. The data presented therein establish that A₆₁ is a novel A-chain fragment. The sequence of the molecule indicates that, unlike angiostatin and other plasminogen fragments purported to inhibit endothelial cell proliferation, A₆₁ consists of the first four kringles of plasminogen plus the kringle 4-kringle 5 linker region and seven residues of kringle 5.

The availability of large amounts of A₆₁ enabled an investigation of the secondary structure of A₆₁. For this purpose, a circular dichroism spectrum was obtained from samples of the molecule (FIG. 8). Circular dichroism (CD) measurements were performed with a Jasco J-810 spectropolarimeter. The spectropolarimeter was calibrated with an aqueous solution of recrystallized ammonium d-10-camphorsulfonate. A₆₁ (0.4-0.6 mg/ml) was incubated in 10 mM Tris-HCl (pH 7.5) and 150 mM NaCl in the presence or absence of ligand for 20 min at room temperature. Samples (0.1 ml) were scanned in a quartz cuvette (0.5-mm path length) from 178 to 260 nm at a rate of 20 nm/min, using a bandwidth of 1 nm and a response time of 4 sec. CD spectra of proteins were obtained by averaging three wavelength scans and were corrected by subtracting buffer scans or, where appropriate, scans of ligand in buffer. Results are expressed as Δε_((M−1·cm−1)). The A₆₁ secondary structure content was assessed with the program CDsstr version 1.8 (Johnson, W. C. (1999) Proteins 35: 307-312).

The far-UV circular dichroism spectrum of A₆₁ exhibited a strong negative band at 202 nm and a weak positive band at about 227 nm. This spectrum is similar to that reported for other kringle containing A-chain fragments such as kringle 4 (Cleary, S., et al. (1989) Biochemistry 28: 1884-1891; Castellino, F. J., et al. (1986) Arch Biochem. Biophys. 247: 312-320; Misselwitz, R., et al (1994) Int. J. Biol Macromol. 16: 187-194.). Analysis of the secondary structure content from CD spectra yields about 21% -strand, 14% -turn, 18% 31-helix, 8% 310-helix, and 40% unordered. Similar to other kringle-containing structures, A₆₁ does not contain any α-helix structure. These results establish that the A₆₁ generated in the cell-free system in the absence of a sulfhydryl donor did not result in the denaturation of the molecule.

FIG. 8 shows the CD spectrum of A₆₁. Wavelength scans were conducted at 20° C. in 10 mM Tris (pH 7.5), 150 mM NaCl. The protein concentration of A₆₁ was 8.5 μM. The line through the points represents the best fit for the data reconstructed from the average of the calculated combinations of secondary structure content.

The absence of •-helical structure in A₆₁ was indicated from analysis of the far-UV CD spectrum using CDsstr, a recently released computer program (Johnson, W. C. (1999) Proteins 35: 307-312). Overall, the secondary structure of A₆₁ is comparable to other kringle-containing proteins. Recently, it was demonstrated that kringle-containing proteins contain significant 3₁-helix. This structure was not reported in earlier x-ray structures because of the difficulty in visualization. However, the far-UV CD spectrum is uniquely sensitive to 3₁-helix. The presence of 3₁-helix in A₆₁ is consistent with the 3₁-helix structures recently reported for other kringle-containing structures such as plasminogen (Marti, D. N., et al., (1999) Biochemistry 38: 15741-15755). Since the intrinsic fluorescence emission spectrum of A₆₁ increased in the presence of lysine or lysine analogues, we have concluded that the kringles of A₆₁ are functionally active.

Intrinsic fluorescence spectroscopy was used to investigate the function of the kringles of A₆₁. Excitation and emission spectra were collected with a Perkin-Elmer Life Sciences LS 50B fluorescence spectrometer equipped with a constant temperature cell holder. The excitation and emission slit widths were set to 5 and 10 nm, respectively. The spectra were collected at 25° C. with A₆₁ (3.7 μM) in a buffer consisting of 20 mM Hepes (pH 7.4) and 140 mM NaCl and in the presence or absence of ligand. The data were corrected for the slight dilution consequent to ligand additions.

FIG. 9 shows the intrinsic fluorescence spectra of A₆₁ in the absence and presence of Trans-4-aminomethylcyclohexanecarboxylic acid (AMCHA). The excitation E_(x) and emission (E_(m)) spectra of ligand-free (solid line) and AMCHA-saturated A₆₁ (dotted line) are presented. The spectra were measured at 20° C. in 20 mM Hepes (pH 7.4) and 140 mM NaCl. The concentration of the A₆₁ was 3.7 μM.

The binding of lysine-type zwitterions such as ε-amino-n-caproic acid to the kringles of plasminogen is known to result in an increase of about 7% in the intrinsic protein fluorescence (Violand, B. N., et al. (1978) J. Biol. Chem. 253: 5395-5401). A₆₁ was therefore examined for shifts in intrinsic fluorescence spectra resulting from contact with potential ligands. FIG. 8 presents the excitation and emission intrinsic fluorescence spectra for A₆₁. The excitation and emission maxima were 283 and 342 nm, respectively. The binding of lysine and other lysine analogues such as ε-amino-n-caproic acid and N-acetyl-L-lysine (which mimics the structure of a C-terminal lysine) caused a significant increase in the intrinsic fluorescence emission spectra. AMCHA caused the largest increase (27%) in fluorescence intensity of the emission spectra. However, N-acetyl-L-lysine methyl ester, a lysine analogue that mimics the structure of an internal lysine residue, did not cause a significant change in the fluorescence emission spectra. These data are summarized in Table III. Because the intrinsic fluorescence emission spectrum of A₆₁ increased in the presence of lyine or lysine analogues, the kringles of A₆₁ are functionally active and can bind to free lysine residues or C-terminal lysine residues but not to internal lysine residues.

EXAMPLE 5

This example illustrates the biological properties of A₆₁.

To examine the effects of A₆₁, on endothelial cell growth, bovine capillary endothelial (BCE) were contacted with A₆₁. For these experiments, cells were grown in DMEM (JRH Biosciences) supplemented with 10% calf serum, 2 mM L-glutamine, 10 units/ml penicillin G, 10 μM streptomycin sulfate, and 3 ng/ml basic fibroblast growth factor (bFGF; Calbiochem). Cells between passages 3 and 5 were then plated into 24-well tissue culture plates (3,000 cells/well) and incubated at 37° C. for 24 h. The medium was then replaced with fresh DMEM containing 5% calf serum in the presence or absence of A₆₁ (generated by the cell-free method) which had been applied to a Detoxi-Gel column (Pierce) to remove endotoxin immediately prior to use. (Endotoxin levels were determined to be less than 45 pg endotoxin per ml (0.4 Endotoxin Units/ml) by the Pyrotell Limulus amoebocyte lysate assay (Associates of Cape Cod, Inc., Falmouth, Mass.)). After a 30-min incubation of the cells in the presence of A₆₁, bFGF was added to a final concentration of 1 ng/ml, and cells were further incubated for 72 h. The cells were trypsinized, resuspended in Isoton II (Beckman), and counted with a Coulter counter.

A₆₁ inhibited BCE cell growth in a dose-dependent manner when the effects of A₆₁ on endothelial cell proliferation were assayed by this method (FIG. 9). The concentration of A₆₁ generated from plasminogen required for 50% inhibition was about 35±10 nM (mean±S.D., n=4) for A₆₁ prepared in the absence of an exogenous sulfhydryl donor. Maximum inhibition of proliferation of the BCE cells was observed at an A₆₁ concentration of about 200 nM. The potency of A₆₁ prepared in the presence of the sulfhydryl donor N-acetyl cysteine was identical. However, the IC₅₀ of 35 nM is significantly lower than the IC₅₀ of 300 nM reported by Soff and co-workers (Gately, S., et al., (1997) Proc. Natl. Acad. Sci. U.S.A. 94, 10868-10872), and thereby represents a significant improvement. Concentrations of A₆₁, as high as 2 μM did not inhibit the proliferation of several nonendothelial cell lines such as HT1080 fibrosarcoma cells, HeLa cells, and 293 cells.

FIG. 10 shows the biological activity of A₆₁. A, inhibition of bovine capillary endothelial cell proliferation. BCE cells were incubated with 1 ng/ml bFGF and various concentrations of A₆₁ which was prepared in the presence (open circles) or absence (closed circles) of the sulhydryl donor N-acetyl cysteine. After 72 hours of incubation, the cells were trypsinized, resuspended in Isoton II solution, and counted with a Coulter counter. B, inhibition of metastatic tumor growth in vivo. Mice were injected intraperitoneally with phosphate-buffered saline (PBS) or A₆₁ (in PBS) (2.5 mg/kg/day) immediately after removal of the primary tumor. The lungs were removed at specific intervals, and the lung weights were compared.

Anti-tumor activity of A₆₁ in vivo was investigated using a Lewis Lung Carcinoma assay (U.S. Pat. No. 5,776,704 to O'Reilly et al). Lewis lung carcinoma cells were grown, harvested at log phase, and resuspended in PBS. Approximately 10⁶ cells were injected subcutaneously in the middle dorsum of 6-8-week-old C57BL/6 male mice. When tumors reached 1500 mm³ in size (about 14 days after implantation), the mice were randomly separated into two groups. The first group underwent surgical removal of the tumor, and the second group was subjected to a sham surgical procedure in which tumors were manipulated but were left intact. Animals from the tumor-resected group were randomly placed into test and control groups. The test group of mice received daily intraperitoneal injections of A₆₁ in PBS (dose =2.5 mg/kg/day), whereas the control group received PBS alone. Every 3rd day after tumor resection, mice were sacrificed, and the lungs were weighed.

The lung weight of the PBS-treated, tumor-resected mice increased over time (FIG. 11). Eighteen days after the tumor resection, lung weight, which correlated with total tumor burden, reached 770±42 mg (n=4). In contrast, the average lung weight of the mice that received daily doses of A₆₁ increased only to 250±14 mg (n=4). The average weights of lungs of normal and 18-day tumor-bearing mice were 191±25 (n=4) and 199±20 mg (n=4), respectively. The increase in the weight of the lungs in the tumor-resected mice corresponded with an increase in the number of observable metastatic foci. These results establish that A₆₁ is a potent anti-tumor agent. While not wishing to be limited by theory, it is believed that the anti-tumor activity is due to the anti-endothelial cell proliferation activity of A₆₁, which manifests as anti-angiogenic activity in vivo. The dosage of 2.5 mg/kg/day which provided for anti-tumor activity is significantly lower than the 15 mg/kg/day used by Soff and co-workers (Gately, S., et al., (1997) Proc. Natl. Acad. Sci. U.S. A. 94, 10868-10872). The increased potency of A₆₁ as an anti-tumor agent thereby represents a significant improvement over other anti-angiogenic plasminogen derivatives.

EXAMPLE 6

This example illustrates the generation of p22 from A₆₁ using cell-free method.

An emerging concept in biology is that certain inactive precursor proteins are cleaved in vivo to produce biologically active fragments. For example, the serine protease kallikrein proteolyses kininogen resulting in the release of bradykinin, a potent vasodilator (Schmaier, 2000 Curr. Opin. Hematol. 7:261-265.). Similarly, the proteolysis of collagen XVIII results in the generation of endostatin, a potent anti-angiogenic protein (O'Reilly et al., 1997 EXS 79:273-294). This concept of bioregulatory proteolysis is dramatically illustrated for plasminogen where the proteolytic cleavage of the molecule can produce either the broad spectrum protease, plasmin or upon further cleavage, anti-angiogenic plasminogen fragments. Although many different plasminogen fragments have been produced in vitro by the proteolytic digestion of plasmin(ogen) or by recombinant technology, it has been unclear what anti-angiogenic plasminogen fragments are produced under physiological conditions. Known anti-angiogenic plasminogen fragments all comprise at least one kringle domain.

Kringle domains are small protein domains that consist of about eighty amino acids and have a characteristic three disulfide-bonded structure. These domains appear to be independently folded units that have been defined structurally to have a cysteine residue at their N- and C-terminus. The kringle domains appear singly in urokinase (Gunzler et al., 1982 Hoppe Seylers. Z. Physiol. Chem. 363:1155-1165.) and factor XII (McMullen and Fujikawa, 1985 J. Biol. Chem. 260:5328-5341), twice in tissue-type plasminogen activator and prothrombin (Pennica et al., 1983), four times in hepatocyte growth factor (Tashiro et al., 1990 Proc. Natl. Acad. Sci. U.S.A. 87:3200-3204), five times in plasminogen and about forty times in apolipoprotein(a) (McLean et al., 1987 Nature 330: 132-137; Castellino and McCance, 1997 Ciba Found. Symp. 212:46-60.; Castellino and Beals, 1987 J. Mol. Evol. 26:358-369). One of the key structures within a kringle is its lysine-binding site. In general, the lysine-binding site of a kringle interacts with the C-terminal lysine residue of the target protein. For example, the kringle domains of plasminogen are presumed to interact with fibrin by binding to an exposed lysine side chain. Furthermore, the kringle domains of plasminogen bind to the cell surface via their binding to the C-terminal lysines of receptor proteins such as annexin II tetramer or to their major plasma inhibitor, α2-antiplasmin (Kassam et al., 1998 Biochemistry 37:16958-16966; Longstaff and Gaffney, 1991 Biochemistry 30:979-986; Christensen et al., 1996 FEBS Lett. 387:58-62). There is also evidence that the kringles are capable of mediation of intramolecular interactions by interacting with intra-chain lysine residues (Ryan and Keegan, 1985 Biochim. Biophys. Acta 830:187-194; Menhart et al., 1995 Biochemistry 34:1482-1488.; McCance and Castellino, 1995 Biochemistry 34:9581-9586; Takada et al., 1993 Thromb. Res. 50:285-294).

The plasminogen kringles have been extensively studied. These structures have 48-50% identity but are not functionally equivalent. For example, the binding affinities of the kringles for N-acetyl-L-lysine, which models the structure of a C-terminal lysine is in order of decreasing affinity is kringle 1>kringle 4>kringle 2. Kringle 5 only weakly binds this lysine analogue while kringle 3 is incapable of binding (Marti et al., 1997). Interestingly, kringle 1, kringle 2, kringle 4 and kringle 5 have similar affinity for lysine analogues that mimic an intra-chain lysine (Marti et al., 1997 Biochemistry 38:15741-15755.). The plasminogen kringles may have distinct binding partners. Kringle 2 exclusively binds to intra-chain lysines of the group A streptococcal surface protein, PAM (Marti et al., 1997 Biochemistry 38:15741-15755). Likewise, kringle 4 exclusively interacts with the C-terminal lysine residue of alpha2-antiplasmin (Christensen et al., 1996 FEBS Lett. 387:58-62).

The present inventors have found cancer and normal cells can convert plasminogen into a novel 22 kDa fragment having anti-tumor activity, p22. p22 is the smallest plasminogen fragment shown to be generated under physiological conditions. Since p22 contains only a single kringle domain, an important benefit of this invention is its simple structure of short amino acid sequence and lack of glycosylation, both of which facilitate further Investigation and production. To date, p22 is the smallest plasminogen fragment that has been shown to be generated under physiological conditions. Since p22 contains only a single kringle domain, future structure-function analysis of the anti-proliferative activity of this protein will be simpler that similar studies of the multiple kringle-containing plasminogen fragments such as A₆₁. The kringle regions of plasminogen have been expressed as recombinant proteins it has been possible to compare their biological activities with that of p22. The individual plasminogen kringle domains have distinct anti-proliferative activities as measured by the endothelial cell proliferation assay. K5, K1 and K3 exhibit potent inhibitory activity, K2 displays weaker activity while K4 is an ineffective inhibitor (Cao et al 1996., J. Biol. Chem. 271:29461-29467; Cao et al., 1997 J. Biol. Chem. 272:22924-22928.). These kringles also have discrete inhibitory functions on endothelial cell migration with K5 and K4 showing potent activity and K2 and K3 showing lesser inhibitory activity and K1 showing negligible activity (Ji et al., 1998 Biochem Biophys Res Commun 247:414-419; Ji et al., 1998 FASEB J. 12:1731-1738.). Interestingly, while the structural integrity of the kringles appears to be necessary for their inhibitory activities the lysine binding site of the kringle does not appear to be involved in their inhibitory activity (Ji et al., 1998 Biochem Biophys Res Commun 247:414-419; Cao et al., 1996 J. Biol Chem. 271:29461-29467).

To generate p22 in a cell-free system, A₆₁, (7 ·M) generated using the cell-free system was incubated with 0.1·M of plasmin and buffer containing 20 mM Hepes (pH 7.4), 140 mM NaCl and 100 μM of dithiothreitol for 2 h at 37° C. The reaction was stopped by adding 1 mM Pefabloc (Roche) and the mixture loaded onto a L-lysine-Sepharose column previously equilibrated with equilibration buffer comprising 20 mM Hepes pH7.4 and 140 mM NaCl. The flow-through fraction collected from the lysine-Sepharose column was loaded onto an octyl-Sepharose resin previously equilibrated with 20 mM Hepes (pH7.4) and 4M NaCl. The flow-through fraction collected from the octyl-Sepharose chromatography yielded milligram quantities (as determined using ultraviolet absorbance as described in Example 1) of an isolated protein having an M_(r) of 22,000 as determined by SDS-PAGE conducted under reducing conditions as described in Example 1. The isolated protein, named p22, was dialyzed against 20 mM Hepes (pH 7.4) and 20 mM NaCl. The dialyzed p22 protein was aliquoted and stored at −70° C. until subsequent use.

FIG. 12 shows the generation of p22 in a cell-free system. A₆₁ (lane 1) was incubated with plasmin (0.1 μM) and dithiothreitol (100 μM) at 37° C. for 2 hours (lane 2). p22 was purified by L-lysine-Sepharose column chromatography (lane 3), concentrated (lane 4), and further purified by octyl-Sepharose column chromatography (lane 5). Samples were subjected to SDS-PAGE, and protein bands were visualized after staining with Coomassie blue.

EXAMPLE 7

This example illustrates the generation of p22 by contacting A61 with cells in vitro.

To generate p22 with the aid of cells, human HT1080 cells were maintained in DMEM (GIBCO-BRL) supplemented with 10% heat-inactivated fetal bovine serum, 10 units/ml penicillin G, and 10 μM streptomycin sulfate. Approximately 1×10⁵ cells in 1 ml were added to each well of 24-well tissue culture plates and incubated at 37° C. for about 24 hours, whereby cell monolayers were formed. The cell monolayers were then washed three times with DMEM, and 0.5-8 μM [Glu]-plasminogen in DMEM was added to each well. After about 18 hours of incubation, the medium was removed and diluted with SDS-PAGE sample buffer with β-mercaptoethanol present as reducing agent, and subjected to SDS-PAGE and Western blot analysis as described in Example 1.

When a monoclonal antibody against human plasminogen kringles 1-3 was used as the primary antibody on the Western blot, a protein having an M_(r) of about 22,000 was detected. Furthermore, upon varying the concentration of plasminogen added to the cells, the amount of p22 varied in a dose-dependent manner. The generation. of p22 was observed at plasminogen concentrations as low as 1 μM, i.e., at approximately the physiological concentration of circulating plasminogen. Similar results were obtained when [Lys]-plasminogen was substituted for [Glu]-plasminogen. Other cells, such as BCE cells and HeLa cells also converted plasminogen to p22. However, human umbilical vein endothelial cells (HUVECs) did not generate detectable p22 under the same experimental conditions. Furthermore, based on its mobility in SDS-PAGE under reducing conditions, p22 is slightly larger than recombinant kringle 1 (rK1) of human plasminogen, yet smaller than the M_(r) of 38,000 or 25,000 determined for recombinant kringle 1-3 or recombinant kringle 2-3, respectively (Rejante, M. R. and Llinas, M. (1994) European Journal of Biochemistry 221: 939-49; An, S. S. et al., (1998) Protein Sci. 7: 1947-1959). It is therefore concluded that p22 is a novel plasminogen fragment comprising a single kringle domain.

FIG. 13 shows the identification of a novel plasminogen fragment (p22) produced by HT-1080 cells. (A) HT1080 cells were incubated with DMEM containing the indicated concentrations of [Glu]plasminogen. After an overnight incubation, the medium was analyzed by 15% reduced SDS-PAGE followed by Western blotting with a monoclonal antibody against human plasminogen kringle 1-3 antibody. [Glu]plasminogen (8 μM) after overnight incubation in the absence of cells (lane 1), and A61 standard (lane 7). The HT1080 cells were incubated with the following concentrations of [Glu]plasminogen: 0.5 μM (lane 2); 1 μM (lane 3); 2 μM (lane 4); 4, μM (lane 5); 8 μM (lane 6). (B) HT1080 cell were incubated with DMEM containing the indicated concentrations of [Lys]plasminogen as indicated in (A). (C) HT1080 cells (lane 5), BCE cells (lane 6), or HUVECs (lane 7) were incubated with DMEM containing 8 μM [Glu]plasminogen, and after an overnight incubation the medium was subjected to SDS-PAGE under reducing conditions in a 12.5% gel, followed by Western blotting using a monoclonal antibody against human plasminogen kringle 1-3. [Lys]plasminogen was used in the case of HeLa cells (lane 8). The following standards are also shown: plasminogen (lane 1); A61 (lane 2); p22 (lane 3); recombinant kringle 1 (lane 4).

EXAMPLE 8

This example discloses biochemical and biophysical properties of p22.

In order to identify the region of plasmin(ogen) that was cleaved to produce p22, HT1080 cell-generated p22 was subjected to N-terminal sequence analysis using Edman degradation. The N-terminus of p22 corresponded to Lys⁷⁸ of plasminogen. However, since p22 is larger than the kringle1 of plasmin(ogen) (FIG. 12), it was concluded that p22 consists of kringle 1 of plasmin(ogen) and additional residues that form the link between the first and second kringles of plasmin(ogen).

p22 generated using the cell-free system was subjected to N-terminal sequence analysis by the methods presented for A₆₁ above. This analysis revealed that its N-terminal amino acid of p22, like A₆₁, is also Lys⁷⁸ as shown in Table IV. Human P22 was generated from human anti-angiogenic plasminogen fragment, A₆₁ and uPA in the cell-free system as described above.

TABLE IV Amino- and Carboxyl-Terminal Sequence of Human p22 Plasminogen G₁₇₆ K₁₇₇ I₁₇₈ S₁₇₉ K₁₈₀ T₁₈₁ P22 C-Sequence K I S K Plasminogen K₇₈ V₇₉ Y₈₀ L₈₁ S₈₂ P22 N-Sequence K V Y L S

Furthermore, p22 produced by incubation of plasminogen with HT1080 cells is indistinguishable by SDS-PAGE from p22 produced using the cell-free system (FIG. 12). C-terminal sequence analysis, performed as described for A₆₁ above, revealed that the C-terminus of p22 generated by plasminogen/cell contact or by using the cell-free system is Lys¹⁸⁰. Thus, p22 is a novel plasminogen fragment extending between Lys⁷⁸ and Lys¹⁸⁰, and is therefore composed of six N-terminal residues, plasminogen kringle 1, three residues of the kringle 1-kringle 2 linker region, and 15 residues of kringle 2.

FIG. 14 is a diagrammatic illustration of the structure of p22. The amino acids are indicated using single-letter abbreviations. The shaded region represents the structure of p22.

The amino acids, the 3 letter abbreviations and single letter abbreviations are as follows: alanine-ala-A; arginine-arg-R; asparagine-asn-N; aspartic acid-asp-D; cysteine-cys-C; glutamine-gln-Q; glutamic acid-glu-E; glycine-gly-G; histidine-his-H; isoleucine-ile-I; leucine-leu-L; lysine-lys-K; methionine-met-M; phenylalanine-phe-F; proline-pro-P; serine-ser-S; threonine-thr-T; tryptophan-trp-W; tyrosine-tyr-Y; valine-val-V.

Mass spectrometry analysis conducted on p22 and recombinant kringle 1 (rK1, a single kringle-comprising fragment of plasminogen, obtained as a gift from Dr. M Llinas, Carnegie Mellon University) by the methods presented for A₆₁ in Example 4 revealed that p22 is not glycosylated. The predicted size of p22 calculated from its amino acid sequence is M_(r) 11,825. In comparison, the molecular weight of p22 as measured using mass spectrometry as described in Example 4 is M_(r) 11,821. The similarity of the molecular weight of p22 calculated from the amino acid sequence with that of the molecular weight derived from mass spectrometry rules out the possibility of glycosylation or other post translational modifications of p22. By contrast, the M_(r) of rK1was 9926 as calculated from the amino acid composition and 9815 by mass spectroscopy. This difference in predicted vs. measured size indicates that recombinant kringle 1 is structurally distinct from p22.

In order to examine the secondary structure of p22 (and rK1for comparison), Circular dichroism (CD) spectra were obtained as described in Example 1. The CD spectrum of p22 showed a positive band at 227.5 nm and strong negative band at 202.7 nm, which is characteristic of a protein devoid of ox-helical structure. The negative ellipticity near 200 nm is consistent with the presence of poly(pro)II helices (3₁ helices) within the secondary structure of p22. Estimation of the secondary structure content of p22 by the variable selection method (Johnson, W. C. (1999) Proteins 35: 307-312) suggested that p22 was composed of approximately 17% 3₁ helix (Table IV). In contrast, recombinant kringle 1 exhibited a positive band at 227.5 nm and a strong negative band at 197.4 nm.

TABLE V Comparison of the secondary structure of p22 and K1 Structure P22 K1 helix 0 3 3₁₀ Helix 3 3 sheet 21 25 -turns 15 7 3₁ Helix 17 19 unordered 43 24

FIG. 15 presents the CD spectrum of p22 and K1. Wavelength scans were conducted at 20° C. in 10 mM Tris (pH 7.5), 150 mM NaCl. The concentration of p22 and K1 were 41 μM and 25 μM respectively. The line through the points represents the best fit for the data reconstructed from the average of the calculated combinations of secondary structure content.

Intrinsic fluorescence spectroscopy was used to investigate the function of the kringle of p22. Intrinsic fluorescence spectra for p22 and rK1were obtained as described in Example 1. The intrinsic fluorescence excitation and emission maxima of p22 were 283 nm and 332 nm, respectively. By contrast, the intrinsic fluorescence excitation and emission maxima of rK1were 283 nm and 229 nm, respectively. The binding of the lysine analogue trans-4-aminomethylcyclohexanecarboxylic acid (AMCHA) to p22 caused a significant increase (22%) in the intrinsic fluorescence emission spectra. Furthermore, although rK1showed an increase in intrinsic fluorescence emission spectra of 20% upon binding to AMCHA, the emission maximum was blue shifted from 339 to 331 nm. These results establish that the kringle domain of p22 is conformationally distinct from that of rK1Although not wishing to be bound by theory, the data suggest that amino acids of the N- or C-terminal domains of p22 interact with and modulate the structure of the kringle domain of p22.

FIG. 16 shows the intrinsic fluorescence spectra of p22 and recombinant K1. The excitation (Ex) and emission spectrum (Em) of ligand-free (solid line) and AMCHA (1 mM) saturated A₆₁ (dotted line) is presented. The spectrum was measured at 20° C. in 20 mM HEPES (pH 7.4) and 140 mM NaCl. The concentration of p22 and K1 were 25 mM and 10 mM respectively.

EXAMPLE 9

This example demonstrates the biological activity of p22.

To examine the effects of p22 on endothelial cell growth, BCE cells were grown and treated as described in Example 1, except that p22 generated by the cell-free method was used in place of A₆₁. It was observed that p22 inhibited the growth of BCE cells in a dose-dependent manner. The concentration of p22 required for 50% inhibition (IC₅₀) was 14.3+/−2.3 nM (mean +/− standard deviation, n=3), and maximum inhibition was observed at a concentration of 50 nM. The IC₅₀ of p22 was lower than IC₅₀=35 nM for A₆₁ and IC₅₀=39.5+/−9.7 nM (mean +/− standard deviation, n=3) determined for recombinant kringle 1.

FIG. 17 demonstrates inhibition of bovine capillary endotheil cell proliferation by p22 and recombinant kringle 1. BCE cells were incubated with various concentrations of p22 or rK1 in the presence of 1 ng/ml basic fibroblast growth factor. After 72 hour incubation, the cells were trypsinized, resuspended inIsoton II solution, and counted with a Coulter counter. The results indicate that p22 is a highly potent inhibitor of bovine capillary endothelial cell proliferation.

To determine whether p22 possess antiangiogenic activity in vivo, the effect of p22 on de novo growth of blood vessels on chick chorioallantoic membranes (CAMs) was examined. For these experiments, three-day-old fertilized white Leghorn eggs (Lillydale, Calgary, Alberta Canada) were cracked, and chick embryos with intact yolks were placed in 100×20 mm culture dishes. After 3 days of incubation in 5% CO₂ at 37° C., disks of methylcellulose containing phosphate-buffered saline (PBS; 137 mM NaCl, 8 μM Na₂ HPO₄, 1.4 mM KH₂PO₄, 2.7 mM KCl, ph 7.4) or 5 μg of p22 (70 82 of 8.3 μM) were implanted on the CAM of embryos. After 48 hours of incubation, embryos and CAMs were analyzed for the formation of avascular zones under the stereomicroscope, and photographs were taken at 40× magnification. Compared with the PBS control, 5 μg of p22 prevented vascular growth under these conditions.

FIG. 18 shows the inhibition of neovascularization on the chick chorioallantoic membrane (CAM) by p22. Methylcellulose disks containing PBS or 5 μg of p22 were implanted on the CAM of 6-day-old chick embryos. After 48 hours, the formation of avascular zones was analyzed. The photographs are representative of 10 experiments. The dotted circles in panels A and C indicate the position of the methylcellulose disks. (A) A CAM treated with a methylcellulose disc containing p22. The area of the avascular zone is marked by arrows. (B) The high-magnification insert of the area marked by “R” in panel A shows the regressed vessels (arrows) in the adjacent area of the avascular zone. (C) A control CAM with a methylcellulose disk containing PBS. These results further indicate that p22 is has antiangiogenic activity.

Anti-tumor activity of p22 in vivo was investigated using a Lewis Lung Carcinoma assay (U.S. Pat. 5,776,704 to O'Reilly et al). Lewis lung carcinoma cells were grown, harvested at log phase, and resuspended in PBS. Approximately 10⁶ cells were injected subcutaneously in the middle dorsum of 6-8-week-old C57BL/6 male mice. When tumors reached 1500 mm³ in size (about 14 days after implantation), the mice were randomly separated into two groups. The first group underwent surgical removal of the tumor, and the second group was subjected to a sham surgical procedure in which tumors were manipulated but were left intact. Animals from the tumor-resected group were randomly placed into test and control groups. The test group of mice received daily intraperitoneal injections of p22 in PBS (dose =2.5 mg/kg/day, i.e., 500 μl of 8.3 μM p22), whereas the control group received PBS alone. After 14 days all mice were sacrificed, the lungs were weighed, and the number of lung metastatic foci were counted.

The lungs of mice treated with PBS after tumor resection had 38+/−4 (mean +/− standard deviation, n=18) metastatic foci while mice treated with p22 had only 3+/−2 (mean +/− standard deviation, n=18) metastatic foci. The lung weight of mice with the primary tumor resected and treated with PBS increased over time and 14 days after primary tumor resection had reached 646.5+/−123 mg (mean +/− standard deviation, n =18). In contrast to the lung weight of mice treated with PBS, the average lung weight of the mice that had received daily doses of p22 only increased to 191.8+/−31 mg (mean +/− standard deviation, n=18). By comparison, the average weights of the lungs from normal mice or 14-day primary tumor bearing mice were 191+/−25 mg (mean +/− standard deviation, n=5) and 199+/−20 mg (mean +/− standard deviation, n=10), respectively. These results establish that p22 is a potent anti-metastatic agent.

FIG. 18 shows inhibition of metastatic tumor growth in mice lungs. Mice were injected intraperitoneally with PBS or p22 (in PBS) (2.5 mg/kg/day) immediately after removal of the primary tumor. p22 treatment inhibited the growth of metastatic foci (A) and blocked an increase in lung weight (B) after removal of the primary tumor. (C) Visual comparison of PBS- or p22-treated mice lungs at 14 days after resection of the primary tumor. Lungs from normal and primary tumor-bearing mice are also shown. While not wishing to be limited by theory, it is believed that the anti-metastatic activity is due to the anti-endothelial cell proliferation activity of p22, which manifests as anti-angiogenic activity in vivo.

EXAMPLE 10

This example illustrates the role annexin II tetramer plays as an extracellular receptor for plasminogen and the involvement of annexin II tetramer in the formation of plasminogen fragments.

The Ca²⁺-binding protein, annexin II tetramer is a major extracellular receptor for plasminogen. This substance regulates the conversion of plasminogen to plasmin and the autoproteolysis of plasmin (Kassam et al., Biochimitry 37, 16958-16966, 1998a; Kassam et al., J. Biol. Chem. 273:4790-4799, 1998b; Fitzpatrick et al., Biochemistry 39:1021-1028, 2000; Kang et al. Trends Cardiovasc. Med. 9:92-102, 1999). These studies have established that annexin II tetramer binds tissue plasminogen actibator, plasminogen and plasmin. We have also found that anti-angiogenic plasminogen fragment A₆₁ binds to annexin II tetramer (see FIG. 20). In this study, the wells of plastic plates were coated with phospholipid, incubated with annexin II tetramer and extensively washed. Various concentrations of ¹²⁵I-A₆₁ were incubated with the annexin II tetramer-coated wells in the absence (filled circles) of presence of 1 mg/ml bovine serum albumin (filled squares) or 10 nM •-aminocaproic acid (open circles).

Since plasminogen or plasmin are the precursors for the anti-angiogenic plasminogen fragments, A₆₁ and p22, any agent that influences the activity of annexin II tetramer or its subunits, annexin II or p11 will affect the production or destruction of the anti-angiogenic plasminogen fragments. For example, HeLa cells in which extracellular annexin II tetramer is decreased due to transfection with an expression vector containing antisense to the p11 subunit of annexin tetramer, show diminished production of p22 (see FIG. 21). In this study, HeLa cells were transfected with an expression vector containing antisense to p11. The HeLa cells were incubated with plasminogen and after the indicated times, the plasminogen fragments were analyzed by SDS PAGE. Interestingly, when the extracellular concentration of the p11 subunit was increased by stably transfecting Hela cells with a p11 sense expression vector, the production of p22 was increased (FIG. 22). It is, therefore, believed that annexin tetramer and/or its annexin II or p11 subunits plays a key role in the efficacy of the anti-angiogenic plasminogen fragments by regulating their formation on the cell surface.

Our in vitro data also supports the conclusion that annexin tetramer participates in the production of A₆₁ and p22. As shown in FIG. 22, the incubation of plasmin with A₆₁ results in the generation of p22 only after addition of annexin tetramer. This suggests that annexin tetramer is necessary for the plasminolytic cleavage of A₆₁ to p22.

Since A₆₁ and annexin tetramer interact as shown in FIG. 22, we believe that annexin tetramer mediates the cytotoxic action of the anti-angiogenic plasminogen fragments on endothelial cells by acting as their extracellular receptors.

In view of the above, it will be seen that the several advantages of the invention are achieved and other advantageous results attained.

As various changes could be made in the above methods and compositions without departing from the scope of the invention, it is intended that all matter contained in the above description be interpreted as illustrative and not in a limiting sense.

All references cited in this specification are hereby incorporated by reference. The discussion of the references herein is intended merely to summarize the assertions made by their authors and no admission is made that any reference constitutes prior art. Applicant reserves the right to challenge the accuracy and pertinency of the cited references. 

1. An isolated polypeptide, wherein the polypeptide consists of the amino acid sequence of SEQ ID NO:1.
 2. An isolated polypeptide, wherein the polypeptide consists of the amino acid sequence of SEQ ID NO:2.
 3. An isolated polypeptide, wherein the polypeptide consists of the amino acid sequence of SEQ ID NO:3. 